Effects of protein kinase inhibitors on the progression of the cell cycle. especially on the initiation of M phase.

从非洲爪蟾未受精卵中提取促成熟因子（MPF）的硫酸铵级分。检测了K252衍生物和星形孢菌素对MPF组分的MPF和cdc 2激酶活性的抑制作用。K252 a和staurosporine抑制MPF活性的IC_（50）分别为15和1.5 μ g/ml，抑制cdc_2激酶活性的IC_（50）分别为3.5和0.4 μ g/ml。K252 b和KT 5926抑制cdc 2激酶活性，IC 50分别为0.15和60 μ g/ml。蛋白激酶抑制剂的抑制作用强弱顺序为K252 b>星形孢菌素> K252 a> KT 5926。因此，cdc 2激酶的性质与其它蛋白激酶的性质显著不同，特别是其对K252 b的敏感性比对K252 a的敏感性大20倍以上。还检查了蛋白激酶抑制剂对导致MPF活化的过程的影响。30 μ g/mlK 252 a和1.5 μ g/mlK 252 b对cdc 2激酶的抑制程度大致相同，但前者抑制cdc 2蛋白的去磷酸化和p110的硫代磷酸化，而后者则无此作用。因此，认为负责MPF激活的蛋白激酶不同于cdc 2激酶本身。对M期起始的抑制作用以Staurosporine最强，其次是K252 a和K252 b。这可能是由于K252 b穿过细胞膜的低渗透性，但也可能是抑制剂作用于cdc 2激酶本身以外的其他靶点。

Ammonium sulfate fraction of maturation-promoting factor (MPF) was prepared from unfertilized eggs of Xenopus laevis. The inhibitory effects of K252 derivatives and staurosporine on MPF and cdc2 Kinase activities of the MPF fraction were examined. K252a and staurosporine inhibited the MPF activity with IC50 of 15 and 1.5 ug/ml, respectively and the cdc2 Kinase activity with IC50 of 3.5 and 0.4 ug/ml, respectively. K252b and KT5926 inhibited the cdc2 kinase activity with IC50 of 0.15 and 60 ug/ml, respectively. The decreasing order of the protein kinase inhibitors in the potency of the inhibitory actions was K252b> staurosporine> K252a> KT5926. Thus, the property of cdc2 kinase is remarkably different from that of the other protein kinases, especially in that its sensitivity to K252b is greater by more than 20 times than to K252a. The effects of the protein kinase inhibitors on the processes leading to the activation of MPF were also examined. Although 30 ug/ml K252a and 1.5 ug/ml K252b inhibited cdc2 kinase approximately to the same extent, the former inhibited the dephosphorylation of cdc2 protein and the thiophosphorylation of p110, whereas the latter did not. Therefore, the protein kinase responsible for the activation of MPF is suggeted to be different from cdc2 kinase itself. As to the inhibitory effects on the initiation of M phase of cultured cells staurosporine was the strongest, followed by K252a and K252b. This may be due to the low permeability of K252b across the cell membrane, but it is also possible that the inhibitors act on other targets than cdc2 kinase itself.