Abnormal phenylalanine hydroxylation and tyrosine oxidation in a patient with acute fulminant liver disease with correction by liver transplantation.

Phenylalanine hydroxylation, tyrosine oxidation, and plasma appearance of phenylalanine and tyrosine were evaluated in a 49-yr-old woman with fulminant non-A, non-B hepatitis and encephalopathy using a continuous intravenous infusion of L-[ring-D5]phenylalanine and L-[U-14C]tyrosine. Despite marked elevations in plasma phenylalanine and tyrosine appearance and normal apparent albumin synthetic rates, phenylalanine clearance and hydroxylation to tyrosine were only 12% and 60%, respectively, of values observed in individuals with normal liver function. Three days after orthotopic liver transplantation, plasma phenylalanine and tyrosine appearances were not markedly changed. Phenylalanine clearance and conversion to tyrosine, however, were restored to normal. In addition, tyrosine oxidation and apparent albumin synthesis were increased. This case report represents the first in vivo demonstration of a selective diminution of enzyme function in an individual with fulminant liver disease. Liver replacement restored aromatic amino acid degradative capacity and increased albumin synthesis.