Brzeska H, Lynch T J, Korn E D
Laboratory of Cell Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892.
J Biol Chem. 1990 Mar 5;265(7):3591-4.
The actin-activated Mg2(+)-ATPase activities of myosins I from Acanthamoeba castellanii are fully expressed only when a single amino acid on their heavy chain is phosphorylated by myosin I heavy chain kinase. Here we show that kinase isolated by a procedure designed to minimize its phosphorylation during purification can incorporate up to 7.5 mol of phosphate/mol of enzyme when incubated with ATP, possibly by autophosphorylation. The rate of phosphorylation is enhanced about 20-fold by phosphatidylserine but is unaffected by calcium ions. Phosphorylation increases the rate at which the kinase phosphorylates the regulatory site of myosin I by about 50-fold. These results suggest that (auto?)phosphorylation may regulate the activity of myosin I heavy chain kinase in vivo. The stimulation of kinase phosphorylation by phosphatidylserine (other phospholipids have not yet been tested) is of particular interest because myosin I has been shown to be tightly associated with membranes, especially the plasma membrane.
只有当棘阿米巴肌球蛋白I重链上的一个氨基酸被肌球蛋白I重链激酶磷酸化时，其肌动蛋白激活的Mg2(+)-ATP酶活性才能完全表达。在这里我们表明，通过一种旨在使纯化过程中磷酸化最小化的程序分离出的激酶，在与ATP孵育时，可能通过自身磷酸化作用，每摩尔酶最多可掺入7.5摩尔磷酸盐。磷脂酰丝氨酸可使磷酸化速率提高约20倍，但不受钙离子影响。磷酸化使激酶磷酸化肌球蛋白I调节位点的速率提高约50倍。这些结果表明，（自身？）磷酸化可能在体内调节肌球蛋白I重链激酶的活性。磷脂酰丝氨酸对激酶磷酸化的刺激作用（尚未测试其他磷脂）特别令人感兴趣，因为已表明肌球蛋白I与膜，尤其是质膜紧密相关。
