Evaluation of the contribution of intracellular protein dephosphorylation process to regulation of the contractility of mammalian smooth muscle tissues'

在哺乳动物肌肉中，微摩尔浓度的冈田酸(OA)是一种强有力的蛋白磷酸酶抑制剂，对肌肉的收缩产生不可逆转的抑制作用。我们观察到，OA的这一作用伴随着肌球蛋白轻链激酶(MLCK)活性的显著下降，而用分离蛋白磷酸酶2B处理肌肉提取物可以部分逆转这种下降。OA完全阻断佛波酯、血小板活化因子和白三烯B4诱导的作用组装，而趋化肽fMLP和优化酵母多糖的作用不受影响。这些结果表明，存在不同的途径来调节中性粒细胞刺激物的应答。利用OA的衍生物，我们研究了OA的化学结构与其对蛋白磷酸酶的亲和力之间的关系。我们发现，对OA分子的某些官能团进行修饰，可以显著地将其还原为磷酸酶。例如，OA的27-羟基对蛋白质脱氢的亲和力显著降低，相当于标准自由能变化相差10-15kJ/mol，这可能意味着27-羟基是蛋白质磷酸酶的结合部位。

In mammalian soomth muscles, micromolar concentrations of okadai acid(OA), a potent protien phosphatase ihibitor, produces an irreversible inhibitory effect on the contractility. We observed that this action of OA is accompanied by a significant decrease in myosin light-chain kinase (MLCK) activety, which is partially reversed by treatment of muscle extracts with isolated protein phosphatase 2A.OA many inhibit the activity of smooth muscle MLCK by increasing the phoisphorylation level of MLCK peortein.In human neutrophils, we examined the effect of OA on the actin assembly caused by various stimulants. OA completely abrogated action assembly induced by phorbol esters, platelet activating factor and leukotriene B4, whereas the effects of the chemotacitic peptide fMLP and opsonized zymosan were unaffected. These results suggest the existence of divergent pathways mediating the resoponse to the neutrophil stimulants.Using derivatives of OA we examined the relationship between the chemical structure of OA and its affinity to protein phosphatases. We found that modifications of some functional groups of the OA molecule resulted in marked reduction of OA to phosphatases. For example, the affinity to protein dehydrogenation of the 27-hydroxyl group of OA.The marked reduction of affinity, which is equivalent to the deference of 10-15 kJ/mol in standard free energy change, may imply that the 27-hydroxyl group serves as a binding site for the protein phosphatases.