Beck W S, Thorndike J
Biochem Biophys Res Commun. 1984 Apr 16;120(1):74-80. doi: 10.1016/0006-291x(84)91415-3.
Investigations of the coenzyme specificity of N5-methyltetrahydrofolate-homocysteine methyltransferases of diverse biological origin revealed previously unrecognized differences between Escherichia coli methyltransferase and the corresponding enzymes of other species. Cyanocobalamin (CNCbl) actively supports methyltransferase in extracts of animal tissues and E. coli. Cobinamide is more active than CNCbl with rat liver methyltransferase; however, it is non-competitively inhibitory with E. coli enzyme. E. coli methyltransferase, but not rat liver enzyme, is competitively inhibited by alpha-ribazole 3'-phosphate and 5,6-dimethyl-benzimidazole, two moieties of the nucleotide loop. This suggests that animal enzyme binds its corrinoid coenzyme at a site on the corrin macro-ring, while E. coli enzyme binds to the nucleotide loop as well as the macro-ring.
对来自不同生物来源的N5-甲基四氢叶酸-同型半胱氨酸甲基转移酶的辅酶特异性研究表明，此前未认识到大肠杆菌甲基转移酶与其他物种相应酶之间的差异。氰钴胺素（CNCbl）能有效支持动物组织和大肠杆菌提取物中的甲基转移酶。辅酶酰胺对大鼠肝脏甲基转移酶的活性比CNCbl更高；然而，它对大肠杆菌酶具有非竞争性抑制作用。大肠杆菌甲基转移酶而非大鼠肝脏酶受到α-核黄素3'-磷酸和5,6-二甲基苯并咪唑（核苷酸环的两个部分）的竞争性抑制。这表明动物酶在钴胺大环的一个位点结合其类咕啉辅酶，而大肠杆菌酶则与核苷酸环以及大环结合。
