Sodium-potassium-activated adenosine triphosphatase: potassium regulation of enzyme phosphorylation. Sodium-stimulated, potassium-inhibited uridine triphosphate hydrolysis.
Sodium-potassium-activated adenosine triphosphatase: potassium regulation of enzyme phosphorylation. Sodium-stimulated, potassium-inhibited uridine triphosphate hydrolysis.
复制标题
钠钾激活三磷酸腺苷酶：酶磷酸化的钾调节。
DOI：
10.1016/s0021-9258(19)45187-9
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发表时间：
1972
期刊：
影响因子：
--
通讯作者：
B. Goodwin
中科院分区：
文献类型：
--
作者：
G. Siegel;B. Goodwin
发现富含钠钾活化腺苷三磷酸酶的电激微粒体可以催化钠刺激、钾抑制的UTP水解。微粒体在（Mg2++ Na+）刺激反应中被[γ-32P]UTP磷酸化，生成酸稳定的磷酸化蛋白。在Mg2+存在的情况下，Na+对磷酸化的刺激与UTP水解的刺激是平行的。K+在0°平行抑制Na+刺激的磷酸化和水解。UTP和Na+各自部分拮抗K+抑制。经部分蛋白水解的磷酸化蛋白产生标记的磷酸肽，其电泳迁移率与经[γ-32P]ATP磷酸化后获得的类似磷酸肽相同。ATP抑制UTP磷酸化和水解反应，而UTP抑制Na+刺激和（Na++ K+）刺激的ATP水解。然而，酶对UTP的亲和力至少比对ATP的亲和力低1000倍。而2,3-二巯基丙醇-亚砷酸盐仅抑制水解，这与其以ATP为底物的作用相似。结果表明，UTP的磷酸化位点与ATP的磷酸化位点是相同的，并且在Na+刺激下UTP或ATP的水解和（Na++ K+）刺激下ATP的水解都是同一个磷酸肽参与的。K+对UTP水解的抑制源于对磷酸化的抑制。因此，K+对酶至少有两种不同的作用：抑制磷酸化，以及众所周知的在ATP存在下的去磷酸化激活。这两种效应都可以用一个模型来解释，在这个模型中，钾酶对核苷酸和Na+的亲和力降低。另一方面，这些降低了脱磷酶对K+的亲和力。从这个角度来看，ATP由于其对酶的亲和力比UTP更大，能够减少K+对磷酸化的抑制，从而允许随后的K+激活酶去磷酸化在循环中进行。
Electroplax microsomes enriched in sodium-potassium-activated adenosine triphosphatase are found to catalyze sodium-stimulated, potassium-inhibited hydrolysis of UTP. The microsomes are phosphorylated by [γ-32P]UTP in a (Mg2++ Na+)-stimulated reaction to yield an acid-stable phosphoprotein. Stimulation of the phosphorylation by Na+in the presence of Mg2+is paralleled by stimulation of UTP hydrolysis. K+inhibits both the Na+-stimulated phosphorylation and hydrolysis in parallel at 0°. UTP and Na+each partially antagonize the K+inhibition. The phosphoprotein upon partial proteolysis yields labeled phosphopeptides which have the same electrophoretic mobilities as similarly obtained phosphopeptides after phosphorylation by [γ-32P]ATP. ATP inhibits the UTP phosphorylation and hydrolytic reactions, whereas UTP inhibits the Na+-stimulated and (Na++ K+)-stimulated ATP hydrolysis. However, the enzyme affinity for UTP is at least 1000 times less than for ATP. Ouabain abolishes the Na+-dependent UTP phosphorylation and hydrolysis, whereas 2,3-dimercaptopropanol-arsenite inhibits only the hydrolysis, which is similar to its action with ATP as substrate. It is concluded that the UTP phosphorylation site is identical with that reactive with ATP and that the same phosphopeptide is involved in the Na+-stimulated hydrolysis of UTP or ATP and the (Na++ K+)-stimulated hydrolysis of ATP.K+inhibition of UTP hydrolysis results from inhibition of phosphorylation. Thus, K+can have at least two separate effects on the enzyme: inhibition of phosphorylation, in addition to the well known activation of dephosphorylation in the presence of ATP. Both of these effects can be explained by a model in which it is assumed that potassium-enzyme has a reduced affinity for nucleotides and Na+. These, on the other hand, reduce the affinity of dephosphoenzyme for K+. In this view, ATP, by virtue of its greater affinity than UTP for the enzyme, is able to reduce the K+inhibition of phosphorylation, thus permitting the subsequent K+activation of enzyme dephosphorylation to follow in cycle.