METHYL‐VITAMIN B₁₂ AS A SOURCE OF METHYL GROUPS FOR THE SYNTHESIS OF ACETATE BY CELL‐FREE EXTRACTS OF CLOSTRIDIUM THERMOACETICUM

Acetogenesis and the Wood–Ljungdahl pathway of CO2 fixation

“…The structure of cobalamin was not determined until 1956 [55]. The initial indication that a corrinoid could be involved in this pathway was based on two key findings: (1) intrinsic factor (known to inhibit vitamin B 12 -dependent reactions) inhibits incorporation of the methyl group of methyl-B 12 into the C-2 of acetate, and (2) in the presence of pyruvate (as an electron and carboxyl group donor), the radioactive methyl group of 14 C-methylcobalamin is incorporated into the methyl group of acetate [56] (Equation 7). These results suggested to Wood and coworkers why they had been unable to isolate intermediates in deproteinated solutions by pulse labeling with 14 CO 2 - the labeled intermediates were bound to cofactors on proteins!…”

“…As described below, Ljungdahl and coworkers isolated and characterized the H 4 folate-dependent enzymes that catalyze the conversion of formate to methyl-H 4 folate [66]. Although a role for cobalamin in acetogenesis was described around 1965 [56, 58], the required cobalamin-containing enzyme was isolated nearly two decades later [67] - the first protein identified to contain both cobalamin and an iron-sulfur cluster [68]. The properties of the H 4 folate- and cobalamin-dependent enzymes involved in the pathway are described below.…”

A Life with Acetogens, Thermophiles, and Cellulolytic Anaerobes

“…Stadtman in turn mentioned that methyl-vitamin B 12 could play a role as methyl donor in acetate synthesis, similar to 14 C-methyl-B 12 as substrate in the synthesis of methionine (31). Stadtman and coworkers soon showed it to be the case (63).…”

Sixty years of research: from soil science and the browning of dried apricots to the biochemistry of metabolism

“…The studies in Lynen's laboratory prompted investigations on the role of vitamin B 12 in the anaerobic metabolism of nicotinic acid, ethanolamine deaminase, and ethylene glycol, and also in the conversion of CO 2 to various products in Clostridium thermoaceticum [11]. The study in Cohen's laboratory prompted studies on the regulation of glutamine synthetase (GS) activity in E. coli.…”