CERTAIN ASPECTS OF TYROSINE METABOLISM IN THE YOUNG. I. THE DEVELOPMENT OF THE TYROSINE OXIDIZING SYSTEM IN HUMAN LIVER 1

Abstract

The major pathway for tyrosine catabolism in the animal is the non-oxidative transamination of tyrosine to p-hydroxyphenylpyruvate and its subsequent oxidation to homogentisate. The homogentisate is oxidized to fumarylacetoacetate (maleylacetoacetate), which is finally hydrolyzed to fumarate (malate) and acetoacetate. The enzyme system responsible for this catabolism, tentatively called the tyrosine oxidizing system, is soluble and a partial purification can be accomplished with high speed centrifugation of homogenates of liver (1) and kidney (2). When these preparations are used it has been observed (3) that one mole of tyrosine will be completely oxidized to one mole of acetoacetate and one mole of fumarate, with the utilization of two moles of oxygen. In order to obtain maximal tyrosine