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A SOLUBLE PREPARATION FROM RAT BRAIN THAT INCORPORATES INTO ITS OWN PROTEINS [ 14 C]ARGININE BY A RIBONUCLEASE‐SENSITIVE SYSTEM AND [ 14 C]TYROSINE BY A RIBONUCLEASE‐INSENSITIVE SYSTEM
Author(s) -
Barra H. S.,
Rodriguez J. A.,
Arce C. 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.tb12108.x
Subject(s) - arginine , tyrosine , ribonuclease , bovine pancreatic ribonuclease , amino acid , biochemistry , sephadex , chemistry , tris , enzyme , rna , gene
— A 100,000 g supernatant fraction from rat brain that was passed through a column of Sephadex G‐25‐40 was able, after addition of some factors, to incorporate [ I4 C]arginine (apparent K m = 5 μM) and [ 14 C]tyrosine (apparent K m = 20 μM) into its own proteins. The factors required for the incorporation of [ 14 C]arginine were: ATP (optimal concentration = 0‐25‐2 μM) and Mg 2+ (optimal concentration 5 mM). For the incorporation of [ I4 C]tyrosine the required factors were: ATP (apparent K m = 0‐75 μM), Mg 2+ (optimalconcentration 8‐16 mM) and K + (apparent K m = 16 mM). Addition of 19 amino acids did not enhance these incorporations. Optimal pHs were: for [ 14 C]arginine and [ 14 C]tyrosine, respectively, 7‐4 and 7‐0 in phosphate buffer and 7–9 and 7‐3‐8‐1 in tris‐HCl buffer. Pancreatic ribonuclease abolished the incorporation of [ 14 C]arginine but had practically no effect in the incorporation of [ 14 C]tyrosine. Furthermore, [ 14 C]arginyl‐tRNA was a more effective donor of arginyl groups than [ 14 C]arginine, whereas [ 14 C]tyrosyl‐tRNA was considerably less effective than [ 14 C]tyrosine. The incorporations of [ 14 C]arginine and [ 14 C]tyrosine into brain proteins were from 25‐ to 2000‐fold higher than for any other amino acid tested (12 in total). In brain [ 14 C]arginine incorporation was higher than in liver and thyroid but somewhat lower than in kidney. In comparison to brain, the incorporation of [ 14 C]tyrosine was negligible in liver, thyroid or kidney. Kinetic studies showed that the macromolecular factor in the brain preparation was complex. The protein nature of the products was inferred from their insolubilities in hot TCA and from the action of pronase that rendered them soluble. [ 14 C]Arginine was bound so that its a‐amino group remained free. Maximal incorporation of [ 14 C]tyrosine in brain of 30‐day‐old rats was about one‐third of that in the 5‐day‐old rat. The changes with postnatal age in the incorporation of [ 14 C]arginine were not statistically significant.