Studies on the Corrinoids and Porphyrins in Streptomycetes

Abstract

This paper deals with the confirmation of the existence of a cobalamin-dependent terminal step in the methionine synthesis, that is, the methyl transfer from N⁵-CH₃-H₄-folate to homocysteine to form methionine, in the cell-free extracts of Streptomyces olivaceus 605.

This transmethylation reaction required a reducing system and S-adenosylmethionine (SAM) as cofactors.

Methionine formation from serine was observed in the cell-free system and thus this reaction is considered to participate in a series of one-carbon metabolism from serine.

Abstract

The formation of corrinoids and porphyrins in S. olivaceus was affected by the addition of the endproducts or intermediates in the biogenesis of tetrapyrrole compounds such as heme and vitamin B₁₂. The addition of vitamin B₁₂ and its related compound to the medium caused an appreciable promotion of porphyrin accumulation and a slight decrease of the de novo synthesis of the vitamin itself. Heme showed a reverse effect on the porphyrin accumulation in contrast to the case of the vitamin. The activity of (δ-amino-levulinic acid (δ-ALA) dehydratase in vitro was hardly affected by the addition of heme or CH₃-B₁₂ to the reaction mixture when the enzyme preparation was obtained from the cells grown in the glycerol medium in which S. olivaceus accumulated much porphyrins. On the contrary, the activity of the enzyme from the cells cultured in the glucose-lactose medium in which less porphyrin was excreted by S. olivaceus was found to be modulated by the addition of heme or CH₃-B₁₂.