Synthesis of substrate analogs of methyltransferases in the vitamin B12 biosynthetic pathway and characterization of their enzymatic products Original Research Article

The specificity toward substrate analogs of the first two methyltransferases in the vitamin B12 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.