[Phenylalanine-4-hydroxylase activity in the liver in viral hepatitis]

Phenylalanine-4-hydroxylase activity was studied in liver tissue, obtained by biopsy from 5 patients with viral hepatitis and from 8 persons without parthological alterations of liver. The enzymatic activity was estimated by formation of 14C-tyrosine in presence and in absence of added cofactor 2-amine-4-hydroxy-6,7-dimethyltetrahydropteridine. Without addition of the cofactor the phenylalanine hydroxylase activity was of the same order of magnitude in liver tissue of the patients and of healthy persons. In presence of the cofactor the enzyme activity in liver of the patients with the hepatitis of moderate severity constituted 44% of the activity found in the control group. The rate of phenylalanine hydroxylation was 0.19 with 10-2 min-1 in patients with hepatitis and 0.5 with 10-2 min-1--in the control group. In severe and moderate forms of viral hepatitis the impairment of phenylalanine metabolism was due to decrease in the activity of phenylalanine-4-hydroxylase in liver tissue.