Oral leukoplakia is oral potentially malignant disorder with an unclear etiology. Emerging evidence indicates a link between metal dyshomeostasis and carcinogenesis. This study is the first to compare serum concentrations of calcium (Ca), magnesium (Mg), selenium (Se), copper (Cu), zinc (Zn), iron (Fe), lead (Pb) and manganese (Mn), as well as the peripheral blood immunological characteristics, between patients with oral leukoplakia and healthy controls, aiming to explore the potential association between metal dyshomeostasis and oral leukoplakia. This cross-sectional-case-control study recruited 89 participants at West China Hospital of Stomatology, including 59 patients with oral leukoplakia and 30 healthy controls. The concentrations of Ca, Mg, Se, Cu, Zn, Fe, Pb and Mn were measured by inductively coupled plasma-mass spectrometry (ICP-MS), and peripheral blood immunological characteristics were quantified using standard clinical chemistry methods. Compared with the control group, the serum Se level in oral leukoplakia patients was significantly decreased and negatively correlated with the degree of dysplasia. However, the Pb level was significantly increased. Patients with oral leukoplakia had abnormal immune function, with significantly decreased percentages of CD3 + T cell and CD8 + T cells, and significantly increased levels of IgA and antinuclear antibodies. Moreover, the Pb was significantly negatively correlated with cellular immunity, while Se was positively correlated with the count of CD8 + T cells. This study indicates a potential association between metal dyshomeostasis and oral leukoplakia, which may be mediated through the immune function, especially abnormal cellular immunity. These findings provide new insights into the etiology and treatment of oral leukoplakia.

Inorganic drugs have a huge impact in medicine, yet their solution behavior in presence of solvents for biological testing is often underestimated, even for clinically established agents. Speciation, hydrolysis, and redox processes can profoundly affect efficacy, safety, and reproducibility, with direct implications for both in vitro and in vivo testing. Here we present a proof-of-concept study highlighting the importance of systematic stability assessment prior to biological evaluation. Four representative metallodrugs were selected to capture diverse oxidation states, coordination geometries, and activation mechanisms: the ruthenium(III) complex NAMI-A, the platinum(II) drug oxaliplatin, the platinum(IV) derivative Hex-Pt, and the experimental gold(I) complex Npx-Au. Although limited in number, this panel demonstrates that meaningful insights can only be obtained through an integrated, multi-technique approach, including methods such as NMR spectroscopy., UV-Vis spectroscopy, and HPLC-MS early degradation events can be reliably detected, optimal storage conditions defined, and misleading experimental outcomes avoided. Our findings emphasize that rigorous stability profiling over time is not optional but essential for accurate dosing, reproducibility, and correct interpretation of preclinical assays. This work establishes a framework for incorporating systematic solution stability evaluation into the development and experimental use of metallodrugs, ensuring more reliable translation from bench to clinic.

Iron is an essential micronutrient and plays a vital role in human nutrition and plant development. In this report, we investigated iron-binding proteins (IBPs) of bread wheat at the sequence and structure levels, utilizing high-throughput systematic computational biology and bioinformatic approaches. We found that out of 133 346 wheat proteins, at least 0.97% could bind with iron ions. The analysis revealed numerous significant differences among these IBPs, which are involved in various biological functions. Most of these proteins are localized in plastids, followed by the endoplasmic reticulum, cell membrane and nucleus. But the most diverse group of IBPs are localized in the nucleus and cytoplasm region, being functionally associated with various biological processes. Out of 321 IBP unique domains, most proteins fall under GT1-Gtf-like, protein kinase domain, secretory peroxidases and CYP1. Further categorization and classification of these shortlisted IBPs revealed that most of these proteins are involved in metabolic processes, with oxidoreductase activity being the most prominent gene ontology molecular function (GO: MF), whereas biological process (GO: BP) enrichment highlighted the involvement of these IBPs in the management of reactive oxygen species. Protein interaction and identification of hub genes revealed further important IBP genes that have the potential to be used as a reference sheet for wet-lab work in the development of molecular markers for biofortification and understanding iron homeostasis in wheat.

X-ray absorption spectroscopy (XAS) is a technique which is frequently used in metallomics research, providing a valuable tool for the elucidation of element-specific electronic and geometric structural information. Recent decades have seen the development of related synchrotron-based X-ray techniques with enhanced analytical capabilities, including X-ray emission spectroscopy (XES), resonant inelastic X-ray scattering (RIXS), and high energy resolution fluorescence detected X-ray absorption spectroscopy (HERFD-XAS). With appropriate experimental configuration, HERFD-XAS can generate spectra with significantly improved spectroscopic resolution and background rejection compared to conventional XAS, providing a substantial advantage in the analysis of dilute analytes in biological samples. These improvements arise from the capability to interrogate selected fluorescence lines with the use of multiple crystal analyzers, minimizing the effects of core-hole lifetime broadening. Herein, we review a range of existing and emerging applications of HERFD-XAS for the study of metals and metalloids in biology and medicine. Direct comparisons of conventional XAS and HERFD-XAS spectra highlight the substantial improvements in resolution, and greater potential for the interpretation of metal speciation in complex and dilute biological samples. We also discuss current challenges with the design of HERFD-XAS experiments.

Iron is an essential metal for almost all living organisms. The major "consumers" of intracellular iron content are a group of proteins that require an iron-sulfur cluster for their functions. It has been shown that iron-sulfur clusters in proteins are assembled by a set of highly conserved proteins using intracellular free iron and L-cysteine as iron and sulfide sources, respectively. Ironically, excess iron is detrimental to cells as free ferrous iron promotes the production of reactive oxygen species via the Fenton reaction. In Escherichia coli, intracellular iron homeostasis is regulated primarily by a global transcription factor Fur (ferric uptake regulator). Since its discovery, it had been assumed that Fur binds ferrous iron to regulate intracellular iron homeostasis, oxidative stress response, and bacterial virulence, among others. However, the proposed "iron-bound" Fur had never been identified in E. coli or any other bacteria. Recent studies have revealed that E. coli Fur binds a unique [2Fe-2S] cluster in response to elevation of intracellular free iron content, and that the [2Fe-2S] cluster in Fur is enzymatically assembled by the iron-sulfur cluster biogenesis machinery. Because Fur also regulates the expression of the genes encoding the iron-sulfur cluster assembly machinery, Fur represents a key link between biogenesis of iron-sulfur clusters and regulation of intracellular iron homeostasis in bacteria.

Novel monoribbed-functionalized iron(II) cage complexes with optically active and/or terminal biorelevant group(s) were designed and prepared by two-step nucleophilic substitution of their mono- and dichloroclathrochelate precursors. The single-crystal XRD structures of all of them and those of known leader iron(II)-centered cage bioeffector and of its reactive monochloroclathrochelate precursor were solved. These experimental data were used for theoretical quantum chemical calculations of electrostatic potentials for their 3D-shaped molecules. This allowed to localize the peripheral (exterior) biorelevant group(s), which are responsible for supramolecular binding of thus designed clathrochelate guests to globular proteins as the hosts. Host-guest binding in aqueous solutions between the unfolded protein macromolecules and all the aforementioned iron(II) complexes was studied by the circular dichroism method. An inherent chirality of the metalloclathrochelates with optically active ribbed substituent and a metal-centered chirality of all the prepared macrobicyclic compounds, induced by their supramolecular clathrochelate-to-protein binding, were observed.

Iron (Fe) and copper (Cu) are crucial micronutrients for plant growth and development. The yellow stripe-like (YSL) proteins play a vital role in the absorption and transport of metal chelates in plants. The YSL genes in tobacco have not been systematically identified and characterized. This study aims to explore the YSL genes in Nicotiana tabacum. A comprehensive set of 17 NtYSL genes were identified and classified into four distinct clades on the phylogenetic tree. The gene structures, characterized by the length and distribution of exons and introns, and protein motifs are relatively conserved. Genomic localization analysis revealed that the NtYSL genes are unevenly distributed across 15 chromosomes, with 11 pairs of homeologous loci identified within the genome. To investigate the functionality of these genes, we analyzed their expression levels in shoots and roots under Fe- and Cu-deficient conditions by real-time quantitative reverse transcription PCR (qRT-PCR), finding that several NtYSL genes are responsive to Cu deficiency or Fe deficiency. This study provides a systematic characterization of the NtYSL gene family in Nicotiana tabacum and offers insights into their potential roles in Fe and Cu homeostasis.

The complex interplay between metal abundance, transport mechanisms, cell distribution, and tumor progression-related biological pathways (e.g. metabolism, collagen remodeling) remains poorly understood. Traditionally, genes and metals have been studied in isolation, limiting insights into their interactions. Recent advances in spatial transcriptomics and elemental profiling now enable comprehensive exploration of tissue-wide metal-gene interactions, though integration remains challenging. In this proof-of-concept study, we investigated metal-dependent signaling within the tumor microenvironment of a unique colorectal cancer (CRC) tumor. We implemented a spatial multimodal workflow which integrated elemental imaging, gene expression, cellular composition, and histopathological features to uncover metals-related pathways through spatially resolved gene expression correlation analyses. Preliminary findings revealed significant associations, for instance: elevated iron correlated with mesenchymal phenotypes located at the tumor's proliferative front, correlating with expression of genes involved in the epithelial-to-mesenchymal transition pathways, and extracellular matrix remodeling. Preliminary observations from this single sample revealed that high copper concentrations were localized to regions of active tumor growth and were associated with increased expression of immune response genes. This proof-of-concept workflow demonstrates the feasibility of integrating elemental imaging with spatial transcriptomics to identify metals-based gene correlates. Future application of this workflow to larger patient cohorts will pave the way for expansive comparisons across the metallome and transcriptome, ultimately identifying novel targets for tumor progression biomarkers and therapeutic interventions.

Manganese (Mn) plays a dual role in the body, acting as an essential trace element and a potential toxicant, the effects of which depend on its levels. In addition to food, exposure can occur through polluted air and contaminated water. Animal studies suggest that increased retention and absorption of Mn might result from iron deficiency, as both share similar physicochemical properties. However, human evidence is incomplete. This study aimed to confirm and expand upon prior findings that iron status influences Mn kinetics in the U.S. female population. The analysis included 1255 non-pregnant females aged 12-49 years with valid urinary and blood Mn and iron measurements as part of the 2015-2018 National Health and Nutrition Examination Survey. Iron status was assessed with a total body iron (TBI) score calculated from measured serum ferritin and the transferrin receptor. Iron deficiency was defined as a TBI score < 0. Demographic and laboratory characteristics (e.g. age and kidney function) were recorded. Among the study participants, roughly 8.8% were found to have iron deficiency. Conversely, 16.9% of participants exhibited blood Mn levels exceeding 1.5 µg/dL, a commonly used reference. On average, blood Mn was approximately 40% higher in subjects considered iron deficient than in their counterparts after controlling for covariates such as race. Those with iron deficiency also had a lower urine-to-blood Mn ratio. The findings suggest that iron-deficient females may have greater Mn accumulation, increasing the risk of Mn toxicity. Further investigations should include male populations to complement the current findings.

Cancer is an intractable global public health problem. The p53 protein encoded by the TP53 is a tumor suppressor, but it is mutated in many tumors, which promotes the initiation and progression of tumors. The mechanisms of p53 regulates tumors are focused on regulating apoptosis, cell cycle arrest, nutrient metabolism, iron metabolism, and redox levels. Copper is a necessary trace element, and abnormal copper homeostasis not only damages the organism but also affects tumor progression. It has confirmed that p53 can bind to copper, respond to copper levels, and regulate copper metabolism. Some anti-tumor mechanisms of copper-related compounds are related to p53. Herein, we focus on reviewing how to regulate copper-binding proteins by p53, as well as its involvement in copper-mediated cell death and tumor drug resistance. It summarizes the pertinent mechanisms of wild-type p53 in regulating cancers via copper metabolism, which aiming to provide new ideas for future cancer therapy.

Corynebacteria are commercially and medically important Gram-positive bacteria that can switch from aerobic to anaerobic respiration in response to low O2 and the availability of nitrate as an alternative electron acceptor. The narKGHJI operon encoding the respiratory nitrate reductase is under the control of a novel regulator, ArnR, which plays a major role in the aerobic/anaerobic respiratory switch. ArnR was previously shown to be an iron-sulfur cluster protein that modulates its DNA binding according to availability of O2. However, previous data suggest that it does not do this directly in response to O2, but instead by sensing nitric oxide (NO), which builds up only under low O2 through the activity of nitrate reductase. Here, we report spectroscopic and mass spectrometric studies of C. glutamicum ArnR and its reactions with O2 and NO. We demonstrate that ArnR is a dimer that binds a [4Fe-4S] cluster in each subunit, and this form of the protein binds tightly to DNA. The [4Fe-4S] cluster of AnrR degrades only very slowly in the presence of O2, consistent with the ability of ArnR to repress nar transcription under aerobic conditions. Reaction with NO results in the formation of mono- and di-nitrosylated forms of the [4Fe-4S] ArnR dimer, which exhibit altered DNA-binding characteristics such that the di-nitrosyl form no longer binds to promoter DNA (i.e. cluster degradation is not required in order to modulate DNA binding). These data are consistent with previous literature and lead us to propose a model for AnrR regulatory function.

Zinc (Zn) is an essential nutrient supporting a range of critical processes. In the yeast Saccharomyces cerevisiae, Zn deficiency induces a transcriptional response mediated by the Zap1 activator, which controls a regulon of ∼80 genes. A subset support Zn homeostasis by promoting Zn uptake and its distribution between compartments, while the remainder mediate an 'adaptive response' to enhance fitness of Zn-deficient (ZnD) cells. The peroxiredoxin Tsa1 is a Zap1-regulated adaptive factor essential for the growth of ZnD yeast. Tsa1 can function as an antioxidant peroxidase, protein chaperone, or redox sensor: The latter activity oxidizes associated proteins via a redox relay mechanism. We previously reported that in ZnD cells, Tsa1 inhibits pyruvate kinase (Pyk1) to conserve phosphoenolpyruvate for aromatic amino acid synthesis. However, this regulation makes a relatively minor contribution to fitness in low Zn, suggesting that Tsa1 targets other pathways important to adaptation. Consistent with this model, the redox sensor function of Tsa1 was essential for growth of ZnD cells. Using a maltose binding protein-tagged version of Tsa1, we identified a redox-sensitive non-covalent interaction with Pyk1, and applied this system to identify multiple novel interacting partners. This interactome implicates Tsa1 in the regulation of critical processes including many Zn-dependent metabolic pathways. Interestingly, Zap1 is a Tsa1 target, as Tsa1 strongly promoted the oxidation of Zap1 activation domain 2 and was required for full Zap1 activity. Our findings reveal a novel posttranslational response to Zn deficiency, overlain on and interconnected with the Zap1-mediated transcriptional response.

The Suf pathway is the most common pathway for bacterial iron-sulfur cluster assembly and uses the SufBC2D complex as a scaffold for cluster formation. In most Gram-negative bacteria, the SufB subunit of SufBC2D accepts a persulfide from the transpersulfurase, SufE, for incorporation into nascent clusters. There is no reported structure for the SufBC2D-E complex and mechanistic details concerning the coordination of persulfide delivery with other SufBC2D activities are unclear. Using the Suf pathway from Escherichia coli as a model system, we report that SufE acts as a noncompetitive inhibitor of SufBC2D ATPase activity with a Ki value of 1.8 ± 0.2 µM. This value corresponds with a KD value of 1.6 ± 0.2 µM for SufE binding to the SufBC2D complex determined by fluorescence polarization. The rate of persulfide transfer from SufE to SufBC2D is impaired in the presence of ATP, suggesting that the two reactions are mutually exclusive. An AlphaFold3 model of the SufBC2D-E complex predicts electrostatic interactions between acidic residues on SufC and basic residues on the N-terminal helix of SufE. SufE variants at the K9 and R16 positions interfere with the ability of SufE to transfer persulfide to SufBC2D and to inhibit SufBC2D ATPase activity. In vivo complementation growth assays show that these SufE variants exhibit a slow-growth phenotype under iron starvation conditions, confirming the connection between SufE and SufC as important for optimal function in the Suf pathway. The mutual exclusivity of persulfide delivery from SufE and SufBC2D ATPase activity suggests an ordered mechanism for cluster assembly.

Ferroptosis, a recently discovered iron-dependent regulated form of cell death, is characterised by lipid peroxidation and oxidative stress. Recent studies suggested that ferroptosis plays a pivotal role in the pathogenesis of chronic obstructive pulmonary disease (COPD), a progressive and irreversible lung disorder, marked by airflow limitation, emphysema, and chronic bronchitis. Cigarette smoke (CS), one of the prominent risk factors for COPD, is known to induce ferroptosis by generating reactive oxygen species (ROS), depleting antioxidant defences, such as glutathione and glutathione peroxidase 4, and disrupting iron homeostasis. These molecular disturbances lead to cell damage, alveolar destruction, and vascular dysfunction, contributing to disease progression and exacerbations. Ferroptosis is also linked with key COPD mechanisms, which are responsible for mitochondrial dysfunction, inflammation, pulmonary hypertension, and CS-induced irregular distribution of iron-binding proteins. A promising therapeutic strategy for mitigating COPD pathogenesis is targeting ferroptosis via iron chelators, lipid peroxide inhibitors, and antioxidant upregulation. Understanding the regulatory mechanisms governing ferroptosis in lung tissue damage could help identify novel biomarkers and effective treatment strategies. This review explores the mechanistic role of ferroptosis in COPD and uncovers the potential intervention methods that may improve clinical outcomes.

The extensive contamination of terrestrial ecosystems with multiple potentially toxic elements (PTEs) necessitates elucidation of plant adaptive mechanisms under combined PTEs stress. This study examines the physiological adaptations, antioxidant regulation, and PTEs allocation patterns in Cunninghamia lanceolata seedlings exposed to lead (Pb) stress (Pb4, 4.0 mg kg-1 Pb; Pb40, 40 mg kg-1 Pb), cadmium (Cd) stress (Cd2, 2 mg kg-1 Cd; Cd20, 20 mg kg-1 Cd), and combined Pb and Cd stress. Results demonstrated concentration-dependent inhibition of biomass production and chlorophyll b biosynthesis under both single and combined PTEs stress conditions. Different responses in superoxide dismutase activity were observed under combined stress compared to the controls, with lower concentration Pb stress causing notably higher enzymatic activation compared to higher concentration Pb stress. Elevated Cd concentrations resulted in significant accumulation of malondialdehyde in leaf tissues, indicating membrane damage. Lead preferentially accumulated in leaves under single Pb stress, while Cd predominantly accumulated in root systems. However, when the plants were exposed to combined Pb and Cd stress, the PTEs translocation pathways in the plants were altered, which resulted in a greater retention of Cd in the stems compared to when the plants were exposed to the single PTE stress. These findings provide insights into species-specific PTE homeostasis mechanisms under polymetallic stress, thereby providing theoretical foundations for the development of phytoremediation strategies in environments contaminated with multiple PTEs.

Characterization of serum metal element concentrations in pregnancy enables the elucidation of relationships with maternal-fetal and neonatal health. Metal elements in the blood serve as essential cofactors for enzymatic reactions and contribute to blood gas homeostasis, hormone synthesis, and physiological immune function for mother and fetus. Sub-optimal concentrations of some metals have been linked to adverse outcomes, including preterm birth, low birth weight, and impaired neurodevelopment. Maternal obesity also adversely influences metabolic status, including metal metabolism, with the potential for a heightened risk of complications at delivery and long-term health issues in offspring. Research on metal element levels in pregnant women with obesity and their effects on pregnancy outcomes is however limited. This study aims to characterize mid-gestation serum concentrations of 18 metal elements in samples from 755 pregnant women with obesity enrolled in the UK Pregnancies Better Eating and Activity Trial (UPBEAT) and identify associations with pregnancy outcomes. We found that calcium concentration tended to decrease with increasing parity, with an estimated reduction of 6.03 mg/L in multiparous participants compared to nulliparous participants (95% CI: -9.50 to -2.57 mg/L, P = 0.001). Additionally, elevated manganese concentrations at mid-pregnancy were associated with an increased incidence of antepartum haemorrhage after 34 weeks (OR: 4.62, 95% CI: 2.06-12.4, P < 0.001), and higher maternal phosphorus levels were linked to neonatal intensive care unit admissions (OR: 2.83, 95% CI: 1.75-4.67, P < 0.001). A future focus on dysregulation of these metal elements is needed to improve understanding of the clinical associations observed.

Iron-sulfur (Fe-S) clusters are ancient and versatile cofactors that drive essential cellular functions, from electron transport to enzyme catalysis. Their intrinsic sensitivity to oxidation has shaped the evolution of specialized Fe-S cluster biosynthetic and protective mechanisms. Recent findings highlight how human Fe-S-binding regulators exploit this cofactor's reactivity to sense iron and oxygen levels, translating environmental cues into appropriate homeostatic responses. Yet, the same redox sensitivity also renders Fe-S cluster proteins and biosynthesis particularly vulnerable to high oxygen tensions, contributing to pathological outcomes. In this minireview, we examine key discoveries illustrating how Fe-S clusters and oxygen intersect to influence both human health and disease. Finally, we discuss how identifying novel Fe-S targets and regulatory circuits may open innovative therapeutic avenues-harnessing oxygen itself as a strategic element in managing relevant disorders.

Zinc(II) ions play manifold roles in human health; dysregulation of zinc homeostasis has been implicated in a number of diseases and pathological conditions. Because zinc(II) is spectroscopically silent, it cannot be detected directly by conventional fluorescence microscopy. As a result, investigators seeking to image zinc(II) in biological systems frequently turn to small-molecule fluorescent sensors that selectively respond to the presence of the ion. This tutorial review describes methods for delivering such small-molecule probes to discrete subcellular locales. Attention is given to the preparation of conjugates in which well-characterized sensors are tethered to molecular homing moieties that accumulate in particular organelles or other compartments. Hybrid approaches that entail enzyme-mediated localization of synthetic constructs, as well as other novel techniques, are also discussed. The various fluorescent probe targeting methods described here enable opportunities for new discoveries in zinc biology.

Iron dyshomeostasis in neurons, involving iron accumulation and abnormal redox balance, is implicated in neurodegeneration. In particular, labile iron, a highly reactive pool of intracellular iron, plays a prominent role in iron-induced neurological damage. However, the mechanisms governing the detoxification and transport of labile iron within neurons are not fully understood. This study investigates the storage and transport of labile ferrous iron Fe(II) in cultured primary rat hippocampal neurons. Iron distribution was studied using live cell fluorescence microscopy with a selective labile Fe(II) fluorescent dye, and synchrotron X-ray fluorescence microscopy (SXRF) for total iron distribution. Fluorescent labeling of the axon initial segment and of lysosomes allowed iron distribution to be correlated with these subcellular compartments. The results show that labile Fe(II) is stored in lysosomes within somas, axons, and dendrites and that lysosomal labile Fe(II) is transported retrogradely and anterogradely along axons and dendrites. In addition, SXRF imaging of total iron confirms iron uptake and iron distribution in the form of iron-rich dots in the soma and neurites. These results suggest that after exposure to Fe(II), labile Fe(II) is stored in lysosomes and can be transported along dendrites and axons. These storage and transport mechanisms could be associated with the detoxification of reactive Fe(II) in lysosomes, which protects cellular structures from oxidative stress. They could also be associated with the metabolic functions of iron in the soma, axons, and dendrites. In this case, easily exchangeable Fe(II) is transported in lysosomes to the neuronal compartments where iron is required.

Pseudomonas aeruginosa is a major contributor to human infections and is widely distributed in the environment. Its ability for growth under aerobic and anaerobic conditions provides adaptability to environmental changes and in confronting immune responses. We applied native 2-dimensional metalloproteomics to P. aeruginosa to examine how use of iron within the metallome responds to oxic and anoxic conditions. Analyses revealed four iron peaks comprised of metalloproteins with synergistic functions, including (1) respiratory and metabolic enzymes, (2) oxidative stress response enzymes, (3) DNA synthesis and nitrogen assimilation enzymes, and (4) denitrification enzymes and related copper enzymes. Fe Peaks were larger under anoxic conditions, consistent with increased iron demand due to anaerobic metabolism and with the denitrification peak absent under oxic conditions. Three ferritins co-eluted with the first and third iron peaks, localizing iron storage with these functions. Several enzymes were more abundant at low oxygen, including alkylhydroperoxide reductase C that deactivates organic radicals produced by denitrification, all three classes of ribonucleotide reductases (including monomer and oligomer forms), ferritin (increasing in ratio relative to bacterioferritin), and denitrification enzymes. Superoxide dismutase and homogentisate 1,2-dioxygenase were more abundant at high oxygen. Several Fe Peaks contained iron metalloproteins that co-eluted earlier than their predicted size, implying additional protein-protein interactions and suggestive of cellular organization that contributes to iron prioritization in Pseudomonas with its large genome and flexible metabolism. This study characterized the iron metalloproteome of one of the more complex prokaryotic microorganisms, attributing enhanced iron use under anaerobic denitrifying metabolism to its specific metalloprotein constituents.