Samizo K, Okagaki T, Kohama K
Department of Pharmacology, Gunma University School of Medicine, Maebashi, Gunma, 371-8511, Japan.
Biochem Biophys Res Commun. 1999 Jul 22;261(1):95-9. doi: 10.1006/bbrc.1999.0956.
Myosin light chain kinase (MLCK) phosphorylates the regulatory light chain of myosin in the presence of Ca(2+) and calmodulin (Ca(2+)-CaM) so that myosin can interact with actin filaments. MLCK has another activity that is not attributable to this kinase activity, i.e., it inhibits the ATP-dependent movement of actin filaments on a myosin-coated glass surface. MLCK itself can be phosphorylated at site A and site B with a few kinases. The phosphorylation at site A reduces kinase activity. However, we have no knowledge as to how phosphorylation of MLCK affects the inhibitory activity of MLCK. When MLCK was phosphorylated at site B, it exerted an inhibitory effect on the movement in much lower concentrations. When Ca(2+)-CaM or ML-9 was present, the inhibition was reduced. The reduction was less when the movement was arrested by the MLCK phosphorylated at site B. This observation was explained by the increase in the affinity of MLCK to myosin upon the phosphorylation at site B.
肌球蛋白轻链激酶（MLCK）在钙离子（Ca(2+)）和钙调蛋白（Ca(2+)-CaM）存在的情况下，使肌球蛋白的调节轻链发生磷酸化，从而使肌球蛋白能够与肌动蛋白丝相互作用。MLCK还有另一种活性，这种活性并非归因于其激酶活性，即它能抑制肌动蛋白丝在包被有肌球蛋白的玻璃表面上依赖ATP的运动。MLCK自身可被几种激酶在A位点和B位点磷酸化。A位点的磷酸化会降低激酶活性。然而，我们并不清楚MLCK的磷酸化如何影响其抑制活性。当MLCK在B位点磷酸化时，它在低得多的浓度下就能对运动产生抑制作用。当存在Ca(2+)-CaM或ML-9时，抑制作用会减弱。当运动被B位点磷酸化的MLCK阻止时，这种减弱程度较小。这一观察结果可以通过B位点磷酸化后MLCK对肌球蛋白亲和力的增加来解释。
