RECENT ADVANCES IN ELUCIDATION OF BIOLOGICAL CORRINOID FUNCTIONS

Eleven adenosylcorrinoid-dependent rearrangements and elimination reactions have been described during the last four decades of vitamin B-12 research. In contrast, only the cobamide-dependent methionine synthase was well established as a corrinoid-dependent methyl transfer reaction. Yet, investigations during the last few years revealed nine additional corrinoid-dependent methyltransferases. Many of these reactions are catalyzed by bacteria which possess a distinct C1 metabolism. Notably acetogenic and methanogenic bacteria carry out such methyl transfers in their anabolism and catabolism. Tetrahydrofolate or a similar pterine derivative is a key intermediate in these reactions. It functions as methyl acceptor and the methylated tetrahydrofolate serves as a methyl donor.