Abstract
Present review describes recent investigations on the intermediates in the biosynthesis of cyclic tetrapyrroles such as heme, chlorophyll, and vitamin B12. Hydroxymethylbilane has been newly found to be the product of the reaction with PBG deaminase and to be the substrate of uroporphyrinogen III cosynthetase. Porphyrinogen carboxy-lyase has been proved to remove carbon dioxide from the four acetate chain of uroporphyrinogen III in stereochemically same manner. The new route to cobyrinic acid, a precursor of vitamin B12' from uroporphyrinogen III is established by synthesis of radioactive pyrroles. It has been demonstrated that methylation by methionine occurrs at C-2 position, first, and succesive ring contraction to corrin macrocycle of vitamin B12 liberates acetic acid arising from C-20 atom and C-20 methyl moiety.
