Choi S C, Bartha R
Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, New Jersey.
Appl Environ Microbiol. 1993 Jan;59(1):290-5. doi: 10.1128/aem.59.1.290-295.1993.
The prominence of sulfate reducers in mercury biomethylation prompted the examination of the methyl carrier and mercury methylation activity of Desulfovibrio desulfuricans LS. There was a low degree of mercury tolerance and a high degree of methylation during fermentative growth; the opposite was true during sulfate reduction. During 2 days of fermentative growth, up to 37% of HgCl2 was methylated at 0.1 micrograms/ml, but only 1.5% was methylated at 10.0 micrograms/ml. Less than 1% of the added HgCl2 was methylated under sulfate-reducing conditions. D. desulfuricans LS radioimmunoassay results were positive for cobalamin. The addition of CoCl2 and benzimidazole to fermentative cultures increased methylation activity. From D. desulfuricans LS grown in the presence of (57)CoCl2, a corrinoid was extracted and purified. High-performance liquid chromatography analysis of the purified extract yielded a single peak with the retention time of cobalamin, and 97% of the (57)Co radioactivity was associated with this peak. Fast atom bombardment and UV and visible spectra of the isolated corrinoid matched those of cobalamin. When methylated with (14)CH3I, the isolated corrinoid methylated Hg(2+) with a 93.9% preservation of (14)C specific activity. We conclude that D. desulfuricans LS methylates mercury via cobalamin (vitamin B12). Under physiological conditions, the enzymatic catalysis of this reaction is likely.
硫酸盐还原菌在汞生物甲基化过程中的突出作用促使人们对脱硫脱硫弧菌LS的甲基载体和汞甲基化活性进行研究。在发酵生长过程中，该菌对汞的耐受性较低，但甲基化程度较高；在硫酸盐还原过程中则相反。在2天的发酵生长过程中，在0.1微克/毫升的浓度下，高达37%的HgCl2被甲基化，但在10.0微克/毫升时，只有1.5%被甲基化。在硫酸盐还原条件下，添加的HgCl2中甲基化的比例不到1%。脱硫脱硫弧菌LS的放射免疫分析结果显示钴胺素呈阳性。向发酵培养物中添加CoCl2和苯并咪唑可提高甲基化活性。从在(57)CoCl2存在下生长的脱硫脱硫弧菌LS中提取并纯化了一种类咕啉。对纯化提取物进行高效液相色谱分析，得到一个与钴胺素保留时间相同的单峰，97%的(57)Co放射性与该峰相关。分离得到的类咕啉的快原子轰击质谱以及紫外和可见光谱与钴胺素的光谱相匹配。当用(14)CH3I进行甲基化时，分离得到的类咕啉使Hg(2+)甲基化，(14)C比活性保留率为93.9%。我们得出结论，脱硫脱硫弧菌LS通过钴胺素（维生素B12）使汞甲基化。在生理条件下，该反应可能由酶催化。
