Arginine, mitochondrial arginase, and the control of carbamyl phosphate synthesis
| Autor: | Luisa Raijman, Chia-Wei Cheung |
|---|---|
| Rok vydání: | 1981 |
| Předmět: |
Male
Ornithine Carbamyl Phosphate Arginine N-Acetylglutamate synthase Submitochondrial Particles Biophysics Mitochondria Liver In Vitro Techniques Biochemistry chemistry.chemical_compound Animals Urea Molecular Biology Arginase biology Acetyl-CoA Molecular biology Rats Kinetics Digitonin chemistry biology.protein Citrulline Carbamates |
| Zdroj: | Archives of Biochemistry and Biophysics. 209:643-649 |
| ISSN: | 0003-9861 |
| DOI: | 10.1016/0003-9861(81)90324-6 |
| Popis: | It has been proposed that arginine may stimulate urea synthesis in vivo by activating amino acid acetyltransferase and thereby increasing the mitochondrial content of acetylglutamate ( K. Shigesada, K. Aoyagi, and M. Tatibana, 1978 , Eur. J. Biochem.85, 385–391); the latter compound activates carbamyl phosphate synthetase (ammonia), the first enzyme in the pathway of urea synthesis. The following findings are relevant in evaluating the significance of this hypothetical control mechanism, (i) Rat liver mitochondria isolated in buffered mannitol contain significant arginase activity. Most of that activity is released from mitochondria suspended in 150 m m KCl; approximately 10% of the arginase remains bound after two washings with 150 m m KCl. The arginase of KCl-washed mitochondria is associated with the outer membrane and is not solubilized by disruption of the mitochondria with digitonin; small fractions of this arginase are solubilized by washing the outer membrane fragments with 150 m m KCl. (ii) The Km values for arginine of the arginase of unwashed and KCl-washed mitochondria, determined at pH 7.4 and 9.5, are in the range of values reported for liver microsomal arginase. Like the latter, mitochondrial arginase is more active at pH 9.5 than at 7.4. Using fresh preparations, mitochondrial arginase activity is not increased by preincubation with 50 m m MnCl2 at pH 7.4. (iii) With 2 m m arginine, the velocity of ornithine generation by mitochondrial arginase is sufficient to maintain high rates of citrulline synthesis from HCO3− and ammonia; the velocities of citrulline synthesis obtained using 2 m m initial arginine and 2 mM initial ornithine were identical. (iv) Preincubation of mitochondria with glutamate, pyruvate (as a source of acetyl CoA), and 0.1 m m or 1 m m arginine increases carbamyl phosphate synthesis 11 and 29%, respectively, over controls containing only glutamate and pyruvate. Since the lowest arginine concentration used (0.1 m m ) is two- to five-fold above that found in liver in vivo, the postulated stimulation by arginine of urea synthesis by way of the activation of amino acid acetyltransferase is likely to be minimal. |
| Databáze: | OpenAIRE |
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