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

Abstract

Summary

1. Oxidation of tyrosine by the tyrosine oxidase system from livers of thiamine-deficient animals is markedly higher than that by preparations from normal animals. 2. After dialysis the activity of the normal preparation cannot be restored by the addition of ascorbic acid, glutathione, or 2,6-dichloro-phenolindophenol (DCPP). The thiamine-deficient preparations are still very active under these conditions, however. 3. Injection of thiamine into normal and deficient animals one day before assay of the livers for tyrosine oxidase has little effect on the high activity of the thiamine-dencient preparations. Feeding a complete ration for 2 weeks to thiamine-dencient animals, however, decreases the activity to the level present in the normal preparations. 4. Inanition produces an increase in tyrosine oxidase activity by liver enzymes. This may be a partial explanation for the fact that thiamine-dencient rats (which are anorexic) possess a higher activity of this enzyme. The reason for the increase under either of these conditions, however, cannot be explained at present.