Synthesis of substrate analogs of methyltransferases in the vitamin B-12 biosynthetic pathway and characterization of their enzymatic products

The specificity toward substrate analogs of the first two methyltransferases in the vitamin B-12 biosynthetic pathway was probed with 15 synthetic porphyrinogens. Several novel methylated chlorins and isobacteriochlorins were isolated and characterized, suggesting the same methylation sequence C-2 > C-7 > C-20 as for the natural substrate, uro'gen III. The results allow us to narrow down possible structural requirements concerning substrate recognition by the methyltransferase enzymes. (c) 2006 Elsevier Ltd. All rights reserved.