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INCORPORATION OF PHENYLALANINE AS A SINGLE UNIT INTO RAT BRAIN PROTEIN: RECIPROCAL INHIBITION BY PHENYLALANINE AND TYROSINE OF THEIR RESPECTIVE INCORPORATIONS
Author(s) -
Barra H. S.,
Arce C. A.,
Rodriguez J. A.,
Caputto R.
Publication year - 1973
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1973.tb07578.x
Subject(s) - phenylalanine , tyrosine , amino acid , enzyme , biochemistry , chemistry , incubation , stereochemistry
— Of seven amino acids studied, glutamic acid and phenylalanine were incorporated in highest amounts into the hot‐TCA‐insoluble material of the 100,000 g supernatant fraction of rat brain homogenate. The system for incorporation of phenylalanine was RNase‐insensitive and required ATP (apparent K m = 0.64 m m ), KC1 (apparent K m = 14 m m ) and MgCl 2 (optimal concentration range 4‐15 m m ). The apparent K m for phenylalanine was 2.9 m m . [ 14 C]Phenylalanine did not undergo modification before incorporation. Tyrosine and phenylalanine inhibited the incorporation, respectively, of [ 14 C]phenylalanine and [ 14 C]tyrosine when incubated simultaneously or successively. The K m and K t (3.3 m m ) values for phenylalanine in the incorporation reaction and as inhibitor of the incorporation of [ 14 C]tyrosine were similar. We suggest that both the enzyme and the acceptor for the incorporation of these two amino acids are the same. [ 14 C]Phenylalanine and [ 14 C]tyrosine entered into COOH‐terminal positions in the reactions described. Brain exhibited a 25‐ to 100‐fold higher capacity to incorporate phenylalanine than that of liver, kidney or thyroid. The acceptor capacity in rat brain rapidly decreased from day 5 to day 15 of postnatal age and then slowly until age 150 days.