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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Research Article|
May 01 1972
Liver phenylalanine hydroxylase activity in relation to blood concentrations of tyrosine and phenylalanine in the rat
Margaret M. McGee;
Margaret M. McGee
1Department of Biological Chemistry, Harvard Medical School, and the Cancer Research Institute, New England Deaconess Hospital, Boston, Mass. 02215, U.S.A.
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Olga Greengard;
Olga Greengard
1Department of Biological Chemistry, Harvard Medical School, and the Cancer Research Institute, New England Deaconess Hospital, Boston, Mass. 02215, U.S.A.
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W. Eugene Knox
W. Eugene Knox
1Department of Biological Chemistry, Harvard Medical School, and the Cancer Research Institute, New England Deaconess Hospital, Boston, Mass. 02215, U.S.A.
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Publisher: Portland Press Ltd
© 1972 The Biochemical Society
1972
Biochem J (1972) 127 (4): 675–680.
Citation
Margaret M. McGee, Olga Greengard, W. Eugene Knox; Liver phenylalanine hydroxylase activity in relation to blood concentrations of tyrosine and phenylalanine in the rat. Biochem J 1 May 1972; 127 (4): 675–680. doi: https://doi.org/10.1042/bj1270675
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