Abstract
Adenyl cobamide (commonly known as pseudovitamin B12) is synthesized by intestinal bacteria or ingested from edible cyanobacteria. The effect of pseudovitamin B12 on the activities of cobalamin-dependent enzymes in mammalian cells has not been studied well. This study was conducted to investigate the effects of pseudovitamin B12 on the activities of the mammalian vitamin B12-dependent enzymes methionine synthase and methylmalonyl-CoA mutase in cultured mammalian COS-7 cells to determine whether pseudovitamin B12 functions as an inhibitor or a cofactor of these enzymes. Although the hydoroxo form of pseudovitamin B12 functions as a coenzyme for methionine synthase in cultured cells, pseudovitamin B12 does not activate the translation of methionine synthase, unlike the hydroxo form of vitamin B12 does. In the second enzymatic reaction, the adenosyl form of pseudovitamin B12 did not function as a coenzyme or an inhibitor of methylmalonyl-CoA mutase. Experiments on the cellular uptake were conducted with human transcobalamin II and suggested that treatment with a substantial amount of pseudovitamin B12 might inhibit transcobalamin II-mediated absorption of a physiological trace concentration of vitamin B12 present in the medium.
Highlights
Vitamin B12 or cobalamin (Cbl) is commonly known as the red-colored vitamin [1]
Considering that absence of transcobalamin II (TCII), these results suggest that (Ade)Cba might competitively inhibit the TCII-mediated addition of (Ade)Cba had no effect on methylmalonyl-CoA mutase (MCM) activity in the absence of TCII, these results suggest that
We characterized the biological activity of (Ade)Cba as a cofactor of methionine synthase (MS) and MCM in mammalian cells. (Ade)OH-Cba did not act as either a coenzyme or an inhibitor for MCM in COS-7 cells (Tables 3 and 4). These results are supported by previous studies, which report that small changes in the base moiety of the lower ligand of Cba noticeably affect the binding of Cba to bacterial and mammalian
Summary
Vitamin B12 or cobalamin (Cbl) is commonly known as the red-colored vitamin [1]. Cbl has a cobalt-coordinated nucleotide, which provides its base (5,6-dimethylbenzimidazole) as the lower axial ligand. Involved in methionine biosynthesis [1], and 50 -deoxyadenosylcobalamin (AdoCbl), a coenzyme of methylmalonyl-CoA mutase (MCM) (EC 5.4.99.2) involved in amino acid and odd-chain fatty acid metabolism in mammalian cells [2,3]. During Cbl deficiency, holo-MCM is significantly reduced. Molecules 2020, 25, x FOR PEER REVIEW methylmalonyl-CoA mutase (MCM) (EC 5.4.99.2) involved in amino acid and odd-chain fatty acid. During Cbl deficiency, holo-MCM is significantly ofreduced and the stable apoenzyme is accumulated [4]. Nearly no apo-MS is observed at any Cbl-status, andthe the apoenzyme stable apoenzyme is accumulated contrast, nearly nowith apo-MS observedthe at any because is extremely labile[4]. Cbl-status, because the apoenzyme is extremely labile [5].
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