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

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Abstract
The tyrosine oxidizing activity of adult human liver and premature infant liver was determined manometrically in homogenates. Results indicated that the activity of adult liver was 10-30 times greater than that of the premature infant liver. Also, the tyrosine oxidizing activity of liver obtained from full term infants was 3-5 times higher than that of premature infant liver. These results were obtained regardless of the standard of reference used. Large quantities of ascorbic acid added to incubated homogenates did not increase the tyrosine oxidizing activity of premature infant liver. The various steps of tyrosine oxidation were studied and it was determined that the apoenzymes of the tyrosine oxidizing system were markedly decreased in the premature infant liver. The addition of the filtrate from boiled and ultra-filtered homogenates of adult liver did not activate premature infant liver. It is concluded that the tyrosine oxidizing system, in regard to apoenzymes, increased in concentration disproportionately to cell growth.