Nagy A, Shuster T A, Rosenberg M D
J Neurochem. 1983 Jan;40(1):226-34. doi: 10.1111/j.1471-4159.1983.tb12675.x.
An ATP-hydrolysing activity on the external surface of intact synaptosomes from chicken forebrain has been investigated. The observed ATPase activity was not due to leakage of the intracellular ATPase activities, of artefacts resulting from breakage of the nerve endings during the incubation and isolation periods, or to possible contamination by other subcellular particles. Disruption of the synaptosomes resulted in an approximately 2.5-fold increase of the basal, Mg2+-dependent ATPase activity, suggesting that the plasma membrane was acting as permeability barrier to the substrate. ATP hydrolysis was maximal (0.8 mumol Pi/min/mg protein) at pH 8.2 in a medium containing either Mg2+ or Ca2+ ions. Ouabain (0.2 mM) and oligomycin (2 micrograms/mg protein) had no appreciable effect on this ATPase activity. Kinetic studies of the enzyme revealed an apparent Km value of ATP of approximately 4 x 10(-5) M. These data are consistent with the view that the observed ATP hydrolysis was being catalysed by an ectoenzyme, i.e., an enzyme in the plasma membrane of the nerve endings with its active site facing the external medium. The rapid hydrolysis of the released ATP is a suspected function for this ecto-ATPase.
对鸡前脑完整突触体外表的ATP水解活性进行了研究。观察到的ATP酶活性并非由于细胞内ATP酶活性的泄漏、孵育和分离期间神经末梢断裂产生的假象，也不是由于其他亚细胞颗粒的可能污染。突触体的破坏导致基础的、Mg2+依赖的ATP酶活性增加约2.5倍，这表明质膜对底物起到了渗透屏障的作用。在含有Mg2+或Ca2+离子的培养基中，pH 8.2时ATP水解最大（0.8 μmol Pi/分钟/毫克蛋白质）。哇巴因（0.2 mM）和寡霉素（2微克/毫克蛋白质）对这种ATP酶活性没有明显影响。该酶的动力学研究表明ATP的表观Km值约为4×10(-5) M。这些数据与以下观点一致，即观察到的ATP水解是由一种外切酶催化的，即神经末梢质膜中的一种酶，其活性位点面向外部介质。释放的ATP的快速水解是这种外切ATP酶的一种推测功能。
