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Novel vitamin B analogues in which the D-ribose moiety of the nucleotide loop was replaced by an oligomethylene group and a trimethylene analogue containing imidazole instead of 5,6-dimethylbenzimidazole as well as cobinamide methyl phosphate were tested for biological activities with Escherichia coli 215, a B- or methionine-auxotroph, and Lactobacillus leichmannii ATCC 7830 as test organisms. A cyano form of 5,6-dimethylbenzimidazolyl tetramethylene, trimethylene and hexamethylene analogues supported the growth of L. leichmannii in this order. 5.6-Dimethylbenzimidazolyl dimethylene and imidazolyl trimethylene analogues did not show B activity and behaved as weak B antagonists when added together with cyanocobalamin. An adenosyl form of the biologically active analogues served as coenzymes for ribonucleotide reductase of this bacterium, whereas that of the inactive analogues did not. The latter acted as weak competitive inhibitors against adenosylcobalamin. ON the contrary, all the analogues did not support the growth of E. coli 215 at all by themselves and inhibited the growth when added with a suboptimum level of cyanocobalamin. A methyl form of the analogues also did not support the growth of E. coli 215, although they served as active coenzymes for methionine synthase of the bacterium. Since unlabeled analogues strongly inhibited the uptake of [H]cyanocobalamin by this bacterium, it seems likely that the analogues exert their anti-B activity toward E. coli 215 by blocking the B-transport system [ABSTRACT FROM AUTHOR]

Methanosarcina barkeri was recently shown to contain two cytoplasmic isoenzymes of methylcobalamin: coenzyme M methyltransferase (methyltransferase 2). Isoenzyme I predominated in methanol-grown cells and isoenzyme II in acetate-grown cells. It was therefore suggested that isoenzyme I functions in methanogenesis from methanol and isoenzyme II in methanogenesis from acetate. We report here that cells of M. barkeri grown on trimethylamine, H/CO, or acetate contain mainly isoenzyme II. These cells were found to have in common that they can catalyze the formation of methane from trimethylamine and H, whereas only acetate-grown cells can mediate the formation of methane from acetate. Methanol-grown cells, which contained only low concentrations of isoenzyme II, were unable to mediate the formation of methane from both trimethylamine and acetate. These and other results suggest that isoenzyme II (i) is employed for methane formation from trimethylamine rather than from acetate, (ii) is constitutively expressed rather than trimethylamine-induced, and (iii) is repressed by methanol. The constitutive expression of isoenzyme II in acetate-grown M. barkeri can explain its presence in these cells. The N-terminal amino acid sequences of isoenzyme I and isoenzyme II were analyzed and found to be only 55% similar. [ABSTRACT FROM AUTHOR]

A vitamin B requiring strain was isolated from Chlostridium cochlearium T-2 C which is known to synthesize various types of vitamin B including methylcobalamin and has an ability to methylate inorganic mercury. The vitamin B auxotroph lacking the mercury-methylating activity showed higher sensitivity to inorganic mercury than its original strain, while the sensitivity of both strains to methylmercury was relatively low and essentially the same. These data seem to present affirmative evidence to postulate the physiological role of methylcobalamin-dependent methylation of mercury to be a process of detoxication. [ABSTRACT FROM AUTHOR]