Purine nucleotide cycle. Evidence for the occurrence of the cycle in brain.
Cell-free extracts of rat brain catalyze the reactions of the purine nucleotide cycle. Ammonia is formed during the deamination but not the amination phase of the cycle. The activity of adenylate deaminase in brain is sufficient to account for the maximum rates of ammonia production that have been reported. The activity of glutamate dehydrogenase is not sufficient to account for these rates of ammonia production. The activities of adenylosuccinate synthetase and adenylosuccinase are nearly sufficient to account for the steady state rates of ammonia production observed in brain. Demonstration of the cycle in extracts of brain is complicated by the occurrence of side reactions, in particular those catalyzed by phosphomonoesterase, nucleoside phosphorylase, and guanase.
D009597:4-Nitrophenylphosphatase / Q000378:metabolism; D000659:AMP Deaminase / Q000378:metabolism; D000227:Adenine Nucleotides / Q000378:metabolism*; D000243:Adenosine Deaminase / Q000378:metabolism; D000263:Adenylate Kinase / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000378:metabolism*; D006148:Guanine Deaminase / Q000378:metabolism; D006150:Guanine Nucleotides / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007292:Inosine Nucleotides / Q000378:metabolism*; D008025:Ligases / Q000378:metabolism; D008190:Lyases / Q000378:metabolism; D008297:Male; D009132:Muscles / Q000201:enzymology; D009708:Nucleotidases / Q000378:metabolism; D009928:Organ Specificity; D011683:Purine-Nucleoside Phosphorylase / Q000378:metabolism; D011770:Pyruvate Kinase / Q000378:metabolism; D051381:Rats; D014969:Xanthine Oxidase / Q000378:metabolism
D000227:Adenine Nucleotides; D006150:Guanine Nucleotides; D007292:Inosine Nucleotides; D014969:Xanthine Oxidase; D011683:Purine-Nucleoside Phosphorylase; D011770:Pyruvate Kinase; D000263:Adenylate Kinase; D009708:Nucleotidases; D009597:4-Nitrophenylphosphatase; D006148:Guanine Deaminase; D000243:Adenosine Deaminase; D000659:AMP Deaminase; D008190:Lyases; D008025:Ligases