Mishima M, Mabuchi I
Department of Biology, School of Arts and Sciences, University of Tokyo.
J Biochem. 1996 May;119(5):906-13. doi: 10.1093/oxfordjournals.jbchem.a021328.
We studied enzymatic activities in sea urchin egg extracts that phosphorylate myosin regulatory light chain (MRLC) from chicken gizzard smooth muscle. The activity in the presence of EGTA showed cell cycle-dependent changes similar to that of histone H1 kinase, namely, it peaked shortly before cleavage, while that in the presence of Ca2+ ions did not show significant change during division cycle. Phosphopeptide mapping revealed that both the sites phosphorylatable by smooth muscle myosin light chain kinase (MLCK sites) and the sites phosphorylatable by protein kinase C (PKC sites) were phosphorylated in the presence or absence of Ca2+ ions. By analyses using an inhibitor of cdc2 kinase, butyrolactone-I, and ion exchange column chromatography, at least three kinases were detected as kinases that phosphorylate MRLC in vitro. These kinases phosphorylated distinct sites on MRLC. The first one, which phosphorylated the PKC sites, was identified as cdc2 kinase. The second one phosphorylated the MLCK sites in the absence of Ca2+ ions. The third one phosphorylated unknown sites. Possible implication of these activities in regulation of cytokinesis is discussed.
我们研究了海胆卵提取物中使鸡砂囊平滑肌肌球蛋白调节轻链（MRLC）磷酸化的酶活性。在存在乙二醇双（2-氨基乙基醚）四乙酸（EGTA）的情况下，该活性表现出与组蛋白H1激酶类似的细胞周期依赖性变化，即在分裂前不久达到峰值，而在存在钙离子的情况下，其在分裂周期中未显示出显著变化。磷酸肽图谱分析表明，在存在或不存在钙离子的情况下，平滑肌肌球蛋白轻链激酶可磷酸化的位点（MLCK位点）和蛋白激酶C可磷酸化的位点（PKC位点）均被磷酸化。通过使用细胞分裂周期蛋白2（cdc2）激酶抑制剂丁内酯-I和离子交换柱色谱进行分析，至少检测到三种激酶可在体外使MRLC磷酸化。这些激酶使MRLC上不同的位点磷酸化。第一种激酶使PKC位点磷酸化，被鉴定为cdc2激酶。第二种激酶在不存在钙离子的情况下使MLCK位点磷酸化。第三种激酶使未知位点磷酸化。本文讨论了这些活性在胞质分裂调控中的可能意义。
