Khatra B S, Printz R, Cobb C E, Corbin J D
Biochem Biophys Res Commun. 1985 Jul 31;130(2):567-73. doi: 10.1016/0006-291x(85)90454-1.
The activity of a purified high molecular weight phosphoprotein phosphatase was inhibited by purified type II cAMP-dependent protein kinase. This effect required cAMP and was obtained in the absence of ATP. The isolated type II regulatory subunits (R-subunits) from several species also inhibited the phosphatase activity in both crude extracts and purified preparations. Half maximal inhibition was observed at 0.06-0.25 microM, well within the physiological range of R-subunit concentrations. The inhibitory potency of R-subunit was greater using the thiophosphorylated form. Limited trypsinization of the R-subunit abolished the inhibitory activity. The C-subunit released the bound cAMP when combined with R-subunit, but the phosphatase did not, implying that the inhibited species is a R.cAMP-phosphatase complex. The results suggest that the R-subunit might have at least one physiological role in addition to inhibition of the C-subunit, i.e., inhibition of phosphatase. The latter would occur only when cAMP is elevated.
纯化的高分子量磷蛋白磷酸酶的活性受到纯化的II型cAMP依赖性蛋白激酶的抑制。这种效应需要cAMP，且在没有ATP的情况下即可出现。从多个物种中分离得到的II型调节亚基（R亚基）也能抑制粗提物和纯化物中的磷酸酶活性。在0.06 - 0.25微摩尔浓度下观察到半数最大抑制，该浓度完全处于R亚基浓度的生理范围内。使用硫代磷酸化形式时，R亚基的抑制效力更强。对R亚基进行有限的胰蛋白酶消化可消除其抑制活性。C亚基与R亚基结合时会释放结合的cAMP，但磷酸酶不会，这意味着被抑制的物质是R.cAMP - 磷酸酶复合物。结果表明，R亚基除了抑制C亚基外可能至少还有一种生理作用，即抑制磷酸酶。后者仅在cAMP升高时才会发生。
