• Molecules and Cells
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• v.46 no.12
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• pp.736-742
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• 2023

NifB, a radical S-adenosylmethionine (SAM) enzyme, is pivotal in the biosynthesis of the iron-molybdenum cofactor (FeMo-co), commonly referred to as the M-cluster. This cofactor, located within the active site of nitrogenase, is essential for the conversion of dinitrogen (N₂) to NH₃. Recognized as the most intricate metallocluster in nature, FeMo-co biosynthesis involves multiple proteins and a sequence of steps. Of particular significance, NifB directs the fusion of two [Fe₄S₄] clusters to assemble the 8Fe core, while also incorporating an interstitial carbide. Although NifB has been extensively studied, its molecular mechanisms remain elusive. In this review, we explore recent structural analyses of NifB and provide a comprehensive overview of the established catalytic mechanisms. We propose prospective directions for future research, emphasizing the relevance to biochemistry, agriculture, and environmental science. The goal of this review is to lay a solid foundation for future endeavors aimed at elucidating the atomic details of FeMo-co biosynthesis.

• Proceedings of the Korean Society of Sericultural Science Conference
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• 2002.10a
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• pp.82-82
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• 2002

No Abstract, See Full Text

• Korean Journal of Plant Resources
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• v.19 no.6
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• pp.706-715
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• 2006

Nitrate reductase deficient (NR) mutant lines were selected indirectly by their resistance to 100mM chlorate in cell cultures of P. parviflora. A total of 585 chlorate resistant lines were confirmed by a second passage on a high concentration of chlorate. Frequency of spontaneous mutation was $9.7{\times}10^{-7}$ in 3 month old suspension-cultured cells, and in non-selective media containing amino acids as sole nitrogen source. The frequency of mutation could be increased up to 11-fold by culture for 12 months. Out of 40 randomly selected calli, 22 were fully deficient in NR. The rest of the clones contained a decreased level of NR activity. Further characterization was carried out in 13 mutant lines which were fully deficient in NR and in 5 mutant lines containing residual (0-7.0%) NR activity, as compared to wild-type cells cultured on the same medium. The $NR^-$ mutants were tentatively classified as defective in the NR apoenzyme (nia-type; 11 mutant lines including the 5 with residual NR activity) or in the molybdenum cofactor (cnx-type; 7 mutant lines) by the XDH activity. The cnx-type could be further classified into two groups. In one group (5 mutant lines) of these, the NR activity could be partially restored by nonphysiologically high (1.0mM) molybdate in the culture medium. Both types of $NR^-$ mutants were unable to grow on minimal medium containing nitrate as sole nitrogen source, but grew well on amino acids. They also proved to be extremely sensitive to the standard medium ($MSP_1$) containing nitrate and ammonium. Shoot regeneration was obtained only in the $NR^-$ mutants, which contained residual NR activity, but they so far have failed to grow into plants.

• Applied Biological Chemistry
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• v.21 no.3
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• pp.137-143
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• 1978

Xanthine oxidase from bovine thyroid glands was found to contain FAD, molybdenum and iron in a ratio 1:0. 36:1. 6. The molecular weight of the thyroid enzyme was similar to that of the milk enzyme when estimated by gel filtration and polyacrylamide gel electrophoresis. The optimum pH for the enzyme activity was 7.8. The pH of the isoelectric point was determined to be 6.2 by electrofocusing. Sodium dodecyl sulfatepolyacrylamide gel electrophoresis experiment indicated that the enzyme was dissociated into subunits and that the molecular weight for the smallest subunit was 65,000 daltons. Absorption spectra were dissimilar between milk and thyroid xanthine oxidase.

• KSBB Journal
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• v.27 no.2
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• pp.75-85
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• 2012

Although, microbial arsenic mobilization by dissimilatory arsenate-reducing bacteria (DARB) and the practical use to the removal technology of arsenic from contaminated soil are expected, most previous research mainly has been focused on the geochemical circulation of arsenic. Therefore, in this review we summarized the previously reported DARB to grasp the characteristic for bioremediation of arsenic. Evidence of microbial growth on arsenate is presented based on isolate analyses, after which a summary of the physiology of the following arsenate-respiring bacteria is provided: Chrysiogenes arsenatis strain BAL-$1^T$, Sulfurospirillum barnesii, Desulfotomaculum strain Ben-RB, Desulfotomaculum auripigmentum strains OREX-4, GFAJ-1, Bacillus sp., Desulfitobacterium hafniense DCB-$2^T$, strain SES-3, Citrobacter sp. (TSA-1 and NC-1), Sulfurospirillum arsenophilum sp. nov., Shewanella sp., Chrysiogenes arsenatis BAL-$1^T$, Deferribacter desulfuricans. Among the DARB, Citrobacter sp. NC-1 is superior to other dissimilatory arsenate-reducing bacteria with respect to arsenate reduction, particularly at high concentrations as high as 60 mM. A gram-negative anaerobic bacterium, Citrobacter sp. NC-1, which was isolated from arsenic contaminated soil, can grow on glucose as an electron donor and arsenate as an electron acceptor. Strain NC-1 rapidly reduced arsenate at 5 mM to arsenite with concomitant cell growth, indicating that arsenate can act as the terminal electron acceptor for anaerobic respiration (dissimilatory arsenate reduction). To characterize the reductase systems in strain NC-1, arsenate and nitrate reduction activities were investigated with washed-cell suspensions and crude cell extracts from cells grown on arsenate or nitrate. These reductase activities were induced individually by the two electron acceptors. Tungstate, which is a typical inhibitory antagonist of molybdenum containing dissimilatory reductases, strongly inhibited the reduction of arsenate and nitrate in anaerobic growth cultures. These results suggest that strain NC-1 catalyzes the reduction of arsenate and nitrate by distinct terminal reductases containing a molybdenum cofactor. This may be advantageous during bioremediation processes where both contaminants are present. Moreover, a brief explanation of arsenic extraction from a model soil artificially contaminated with As (V) using a novel DARB (Citrobacter sp. NC-1) is given in this article. We conclude with a discussion of the importance of microbial arsenate reduction in the environment. The successful application and use of DARB should facilitate the effective bioremediation of arsenic contaminated sites.

• Journal of Microbiology and Biotechnology
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• v.27 no.3
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• pp.591-597
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• 2017

Maribacter dokdonensis DSW-8 was isolated from the seawater off Dokdo in Korea. To investigate the genomic features of this marine bacterium, we sequenced its genome and analyzed the genomic features. After de novo assembly and gene prediction, 16 contigs totaling 4,434,543 bp (35.95% G+C content) in size were generated and 3,835 protein-coding sequences, 36 transfer RNAs, and 6 ribosomal RNAs were detected. In the genome of DSW-8, genes encoding the proteins associated with gliding motility, molybdenum cofactor biosynthesis, and utilization of several kinds of carbohydrates were identified. To analyze the genomic relationships among Maribacter species, we compared publically available Maribacter genomes, including that of M. dokdonensis DSW-8. A phylogenomic tree based on 1,772 genes conserved among the eight Maribacter strains showed that Maribacter speices isolated from seawater are distinguishable from species originating from algal blooms. Comparison of the gene contents using COG and subsystem databases demonstrated that the relative abundance of genes involved in carbohydrate metabolism are higher in seawater-originating strains than those of algal blooms. These results indicate that the genomic information of Maribacter species reflects the characteristics of their habitats and provides useful information for carbon utilization of marine flavobacteria.

• Journal of Life Science
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• v.17 no.7 s.87
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• pp.990-995
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• 2007

We tested the effect of sodium tungstate, which disturbs the molybdenum cofactor formation, on the activities of aldehyde oxidase(AO) and the growth of maize(Zea mays) primary roots. As reported in other plants, sodium tungstate inhibited AO also in the maize root concentration-dependently. The inhibitory effect of sodium tungstate was observed only when the inhibitor was applied to the living plants. Application of tungstate to the extracted protein did not show any effect. Western analysis revealed slightly decreased level of AO protein in the presence of tungstate, indicating a positive feedback of gene regulation by the product. We also tested the effects of tungstate on the root growth. The elongation of primary root and the development of lateral roots, which are sensitive to the absolute level of auxin, were decreased in the presence of sodium tungstate. However, the gravitropic curvature of the primary root, which is dependent on the relative amount of auxin at both sides, was unaffected. These data suggested the decrease of auxin biosynthesis by the application of tungstate. However, the level of free IAA was unaffected by tungstate application. We discuss the possible explanations for the observed results.