The enzymic phosphorylation of vitamin B1

Publisher Website
Google Scholar
Abstract
A soluble yeast protein was prepared from which cocarboxylase was removed by acidification in presence of ammonium sulphate. The addition of cocarboxylase produced a vigorous decarboxylation of pyruvic acid. Vit. B1 had no stimulating effect even if added to quantities of cocarboxylase well below saturation. Vit. B1 and its mono-phosphate are quite inactive as coenzymes of carboxylase but become very active in presence of adenyl pyrophosphate. Vit. B1-monophosphate was slightly inferior in activity to vit. B1; the monophosphate is thus not an intermediary of the synthesis and must first be hydrolysed to the un-phosphorylated vit. Adenyl pyrophosphate alone has a small catalytic action in combination with the carboxylase protein. This is probably due to the adenyl pyrophosphate''s attaching itself to the enzyme and forming a "pseudo-car-boxylase." In support of this a competitive inhibition was observed if adenyl pyrophosphate was added in large excess over cocarboxylase. Phosphopyruvic acid can act as phosphate donator for the synthesis of cocarboxylase in presence of catalytic amts. of adenylic acid or adenyl pyrophosphate. The synthesis of cocarboxylase stops when the carboxylase protein is partly or fully saturated. No preparative use can therefore be made of the reactions described.

This publication has 2 references indexed in Scilit: