Creatine phosphokinase in mammalian brain

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Abstract
Homogenates of mammalian brain were found to split phosphocreatine in the presence of adenylic acid. The phosphokinase activity of brain homogenates can be recovered in the supernatant on centrifuging them. Mg++ at 0.001_0.002 M are necessary for full activity of the dialyzed enzyme prepns.; Mn and Ca ions are also effective as activators though less so than Mg. K+ is inactive in this respect. The pH optimum of the enzyme for the forward reaction, i.e. the splitting of phosphocreatine in the presence of adenylic acid, lies in the range of 5.9_7; phosphocreatine is split optimally at the same pH range when adenosinediphosphate is used as the phosphate acceptor. Prepns. from brain also catalyze the synthesis of phosphocreatine from creatine and adenosinetriphosphate above pH 8.2. None of the drugs of central action which were examined had any significant effect on the activity of the enzyme. Iodo-acetate inhibited it completely above a concn. of 0.0005 M and fluoride to a much less marked degree.