Cooper P H, Hawthorne J N
Biochem J. 1975 Sep;150(3):537-51. doi: 10.1042/bj1500537.
Tthe properties of diphosphoinositide and triphosphoinositide phosphatases from rat kidney homogenate were studied in an assay system in which non-specific phosphatase activity was eliminated. The enzymes were not completely metal-ion dependent and were activated by Mg2+. The detergent sodium deoxycholate, Triton X-100 and Cutscum inhibited the reaction; cetyltrimethylammonium bromide only activated when added with the subtrates and in the presence Mg2+. Both enzymes had a pH optimum of 7.5. Ca2+ and Li+ both activated triphosphoinositide phosphatase, but Ca2+ inhibited and L+ had little effect on diphosphoinositide phosphatase. Cyclic AMP had no effect on either enzyme. The enzymes were three times more active in kidney cortex than in the medulla. On subcellular fractionation of kidney-cortex homogenates by differential and density-gradient centrifugation, the distribution of the enzymes resembled that of thiamin pyrophosphatase (assayed in the absence of ATP), suggesting localization in the Golgi complex. However, the distribution differed from that of the liver Golgimarker galactosyltransferase. Activities of both diphosphoinositide and triphosphoinositide phosphatases and thiamin pyrophosphatase were low in purified brush-border fragments. Further experiments indicate that at least part of the phosphatase activity is soluble.
在一个消除了非特异性磷酸酶活性的测定系统中，对大鼠肾脏匀浆中二磷酸肌醇磷酸酶和三磷酸肌醇磷酸酶的性质进行了研究。这些酶并非完全依赖金属离子，且可被Mg2+激活。去污剂脱氧胆酸钠、Triton X - 100和Cutscum抑制该反应；十六烷基三甲基溴化铵仅在与底物一起添加且存在Mg2+时才激活反应。两种酶的最适pH均为7.5。Ca2+和Li+均激活三磷酸肌醇磷酸酶，但Ca2+抑制二磷酸肌醇磷酸酶，而Li+对其影响不大。环磷酸腺苷对这两种酶均无作用。这些酶在肾皮质中的活性是髓质中的三倍。通过差速离心和密度梯度离心对肾皮质匀浆进行亚细胞分级分离时，这些酶的分布类似于硫胺素焦磷酸酶（在无ATP的情况下测定），提示其定位于高尔基体复合物。然而，其分布与肝脏高尔基体标记物半乳糖基转移酶的分布不同。在纯化的刷状缘片段中，二磷酸肌醇磷酸酶、三磷酸肌醇磷酸酶和硫胺素焦磷酸酶的活性均较低。进一步的实验表明，至少部分磷酸酶活性是可溶的。
