Dietary Conditions Affecting Oxidation of Tyrosine by Rat Liver, with Particular Reference to Thiamine.

Abstract

Oxidation of tyrosine by the tyrosine oxidase system from livers of thiamine-deficient animals is markedly higher than that by preparations from normal animals. After dialysis activity of the normal preparation could not be restored by addition of ascorbic acid, glutathione, or 2,6-dichlorophenolindophenol (DCPP), and the thiamine-deficient preparations were still very active. Injection of thiamine into normal and deficient animals one day before assay had little effect on high activity of the thiamine-deficient preparations. Feeding a complete ration for 2 weeks decreased the activity to the level present in the normal preparations. Inanition produced an increase in tyrosine oxidase activity by liver enzymes. This may partly explain the higher activity of this enzyme in thiamine-deficient rats (which are anorexic).