Metabolic basis of hypertyrosinemia in liver disease.

Serum tyrosine concentrations in patients with liver cirrhosis and with advanced fatty degeneration of the liver were 143 and 140 mumol/L, respectively, as compared with 65 mumol/l in normal controls. In biopsy samples of histologically normal livers, total tyrosine aminotransferase activity was 10.5 +/- 1.8 nmol p-hydroxyphenylpyruvate formed/mg of protein per min (mean +/- SEM; n = 10) whereas the corresponding figures for 7 cirrhotics were 4.95 +/- 0.85. The enzyme activity was normal in moderate adipose degeneration of the liver, but it was reduced when more than 50% of the hepatocytes were occupied by fat. It is suggested that the hypertyrosinemia of cirrhotics is, at least in part, due to decreased tyrosine aminotransferase activity.