Effect of vitamin B6 deficiency on the basal and adapted levels of rat liver tyrosine and tryptophan transaminases.

Tyrosine-ol-ketoglutarate transaminase activity in the liver was increased several-fold by the injection of hydrocortisone or L-tyrosine into the rat (1,2). Since the activity of this enzyme was measured with an excess of its coenzyme, pyridoxal-P, it was assumed that the increase in the activity represented an increase in the concentration of the protein moiety of the transaminase. Few enzymes with dissociable coenzymes have been found to respond adaptively in their levels. The purpose of the present investigation was to determine whether the protein moiety of an enzyme could be induced under conditions which did not permit all of the enzyme molecules to acquire catalytic function, i.e. during deficiency of the coenzyme. For comparison, three other transaminases in the same organ were also studied. These were tryptophan-or-ketoglutarate transaminase, phenylalanine-pyruvate transaminase, and histidine-pyruvate transaminase (3).