Properties of Myosin ATPase from Whelk Neptunea polycostata Smooth Muscle

Abstract

Myosin was purified from retractor smooth muscle of whelk, Neptunea polycostata.
Ca-, Mg-, and EDTA-ATPase profiles of whelk myosin were studied under various conditions, and compared with those of other myosin, especially Abalone Haliotis discus retractor smooth muscle myosin. The properties of whelk myosin ATPase were almost similar to those of abalone and scallop myosin, though the following differences were observed.
1. At neutral pH and 25°C, enzymatic activities of whelk myosin were lower than those of abalone and scallop myosin.
2. Ca-sensitivity of whelk myosin was higher than that of scallop myosin.
3. In the absence of Ca²⁺, Mg-ATPase activity did not depend on KCl concentration in contrast to rabbit skeletal muscle myosin, scallop myosin and abalone myosin.
4. The pH dependent activity curves under the low ionic condition (0.05M KCl) were different from those of abalone myosin.
5. Arrhenius plots of whelk myosin ATPase activities showed no bending in the temperature range between 5°C and 30°C, which were similar to the case of abalone myosin, but different from scallop myosin. The activation energies were higher for whelk myosin than those for abalone myosin.