개의 대뇌후두엽 조직의 Guanine Aminohydrolase에 관한 연구

Abstract

Crude preparation of the guanine aminohydrolase was obtained from the occipital lobe tissue of dog brain by means of salting-out with ammonium sulfate, and the enzymatic properties were observed with the following conclusions. (l) The KM value of the crude GDA toward the substrate. guanine, was 0.26mM. (2) The GDA was highly heat-stable. and inactivated by urea and guanidine-Hfll, the magnitude of the inhibition by the latter being more prominant than the former. (3) The GDA had a single and broad spectrum of its pH-versus activity profile, ranging from pH 7.0 to 9.0. (4) Among the inorganic ions examined, Cat, Cu++, Mrrr", Fet", Fe+++, Pb!', Co":", CN- displayed no effect on the GDA activity, whereas Hgtt showed 100% and Mgtt about 10% inactivation of the enzyme. (5) There was no evidence of the presence of the natural inhibitor of the present GDA in the mitochondrial fraction of the tissue of the occipital lobe of dog brain, and of product inhibition by xanthine and hypoxanthine as well. (6) There was an indication of possible allosteric property in the present preparation of GDA with GTP as its positive modifier against the alleged cooperative phenomenon.