Betaine Stimulation of Vitamin B12 Biosynthesis in Pseudomonas denitrificans May Be Mediated by an Increase in Activity of -Aminolaevulinic Acid Synthase

Abstract

The stimulation by betaine of vitamin B12 and extracellular coproporphyrin production in the industrial species Pseudomonas denitrificans GY57/2 was confirmed using a replacement culture technique; biosynthesis of haem was also found to be stimulated. In the absence of betaine, δ-aminolaevulinic acid synthase decreased in specific activity from time zero. In the presence of betaine, the enzyme activity increased markedly after 3 h and then decreased after exhaustion of extracellular betaine. The peak specific activity of δ-aminolaevulinic acid synthase increased in a dose-dependent manner. The enzyme was inhibited by haem. δ-Aminolaevulinic acid dehydratase was present in considerable excess over δ-aminolaevulinic acid synthase under all conditions studied and its specific activity was not affected by the addition of betaine. Our tentative conclusion is that the betaine effect is exerted via some positive effect on δ-aminolaevulinic acid synthase, the initial, rate-limiting and very labile enzyme of porphyrin and corrin biosynthesis.