The inhibitory Ca2+-regulation of the actin-activated Mg-ATPase activity of myosin from Physarum polycephalum plasmodia.

摘要: Myosin was rapidly prepared from the slime mould, Physarum polycephalum to a high level of homogeneity (greater than 95%), in yield (about 10 mg/100 g tissue) and phosphorylated state 5 mol phosphate/mol 500,000 Mr myosin). Actin activated Mg-ATPase activity this myosin absence Ca2+ about 30-fold, actin-activated ATPase reduced 20% original when concentration increased 50 microM, i.e., actin-myosin-ATP interactions show Ca-inhibition. The giving half-maximum inhibition 1-3 microM. Ca-inhibition clearly observed at physiological concentrations Mg2+ but obscured both lower higher Mg2+. Ca-inhibitory effect on ATP hydrolysis by actomyosin reconstituted skeletal actin quick reversible. Ca-binding measurement showed that bound with half-maximal binding 2 microM maximum per myosin, indicating may inhibit myosin. involvement myosin-linked regulatory system -control cytoplasmic streaming is discussed.