Li M, Damuni Z
Department of Cellular and Molecular Physiology, Pennsylvania State University, College of Medicine, Hershey 17033.
Biochem Biophys Res Commun. 1994 Jul 29;202(2):1023-30. doi: 10.1006/bbrc.1994.2031.
The catalytic C subunit of protein phosphatase 2A2 was methylated with an apparent km of about 0.1 microM by purified preparations of a methyltransferase from bovine brain. This methylation was inhibited by okadaic acid and microcystin-LR half-maximally at 40 nM and 60 nM, respectively. The extent of inhibition depended on the protein phosphatase concentration in the incubations, but was independent of the methyltransferase concentration. The results demonstrate that okadaic acid and microcystin-LR directly inhibit the methylation of protein phosphatase 2A. The results are consistent with the idea that okadaic acid and microcystin-LR act, at least in part, by binding to the carboxyl terminus of the C subunit of protein phosphatase 2A thereby preventing access of the methyltransferase to its target site, the C subunit carboxyl terminal Leu309.
蛋白磷酸酶2A2的催化C亚基被来自牛脑的甲基转移酶纯化制剂甲基化，表观Km约为0.1微摩尔。冈田酸和微囊藻毒素-LR分别在40纳摩尔和60纳摩尔时对这种甲基化产生半数最大抑制。抑制程度取决于孵育中的蛋白磷酸酶浓度，但与甲基转移酶浓度无关。结果表明，冈田酸和微囊藻毒素-LR直接抑制蛋白磷酸酶2A的甲基化。这些结果与以下观点一致，即冈田酸和微囊藻毒素-LR至少部分地通过与蛋白磷酸酶2A的C亚基羧基末端结合来起作用，从而阻止甲基转移酶接近其靶位点，即C亚基羧基末端的Leu309。
