Figure 1.

Bioconversion (% radiochemical yields) of factors II and III, (and their 3 and 8 epimers) derived from labeled ALA and AdoMet and of factor IV into cobyrinic acid (5) using cell-free extracts of Pr. shermanii. Labeling patterns were derived from either stable isotopes (•, [4-¹³C]ALA; ▪, [5-¹³C]ALA; ∗, [methyl-¹³C]AdoMet) or radioisotopes (•, [4-¹⁴C]ALA; ∗, [methyl-³H]AdoMet) as described in the text. The intermediates are isolated as methyl esters and reincubated (after hydrolysis) in their oxidized forms (factors II–IV) but it is assumed that the biotransformations occur at the reduced (precorrin) level since precorrin-2 can be isolated anaerobically from Pr. shermanii (9).