Polyamine biosynthesis and vitamin B6 deficiency. Evidence for pyridoxal phosphate as coenzyme for S-adenosylmethionine decarboxylase.

Abstract

Extracts of liver from vitamin B 6 -deficient rats had only 50% of the S -adenosylmethionine decarboxylase activity of extracts of liver from control rats when assayed with no exogenous pyridoxal phosphate. When pyridoxal phosphate was included in the reaction mixture, both extracts exhibited the same activity, indicating that pyridoxal phosphate is the coenzyme for S -adenosylmethionine decarboxylase. There was no similar decreased activity in extracts of brain from vitamin B 6 -deficient rats. The activity of the pyridoxal phosphate-dependent enzyme, ornithine decarboxylase, was increased in extracts of liver from vitamin B 6 -deficient rats: 1.6-fold when assayed with no pyridoxal phosphate and 4-fold when assayed with pyridoxal phosphate. The concentrations of putrescine and spermidine were decreased 50% in liver of vitamin B 6 -deficient animals, but only putrescine was decreased in brain. Putreanine was barely detectable in liver of vitamin B 6 -deficient animals, but was unchanged in brain.