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. 1972 May;127(4):675–680. doi: 10.1042/bj1270675

Liver phenylalanine hydroxylase activity in relation to blood concentrations of tyrosine and phenylalanine in the rat

Margaret M McGee 1,*, Olga Greengard 1, W Eugene Knox 1
PMCID: PMC1178765  PMID: 4265522

Abstract

The plasma concentration of phenylalanine and tyrosine decreases in normal rats during the first few postnatal days; subsequently, the concentration of phenylalanine remains more or less constant, whereas that of tyrosine exhibits a high peak on day 13. The basal concentrations of the two amino acids were not altered by injections of thyroxine or cortisol, except in 13-day-old rats, when an injection of cortisol decreased the concentration of tyrosine. In young rats (13–15 days old), treatment with cortisol increased the activity of phenylalanine hydroxylase in the liver (measured in vitro) and accelerated the metabolism of administered phenylalanine: the rate constant of the disappearance of phenylalanine from plasma and the initial increase in tyrosine in plasma correlated quantitatively with the activity of phenylalanine hydroxylase in the liver. In adult rats, the inhibition of this enzyme (attested by assay in vitro) by p-chlorophenylalanine resulted in a proportionate decrease in tyrosine formation from an injection of phenylalanine. However, the quantitative relationship between liver phenylalanine hydroxylase activity and phenylalanine metabolism within the group of young rats was different from that observed among adult rats.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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