Untitled research work

Enzymatic properties of squid mantle myosin were studied in terms of Ca-, Mg- and EDTA-ATPase activities under various conditions, and compared with those of rabbit skeletal myosin. All ATPase activities of squid myosin were very similar to those of rabbit myosin in their pH and KCI concentration dependencies, with the exception of the KCI dependency of the Mg-ATPase activity. Activation energies of all ATPae activities estimated from the ARRHENIUS plot of ATPase activity were found to be identical for myosins from squid and rabbit, with the exception of that of EDTA-ATPase. Squid myosin showed an initial burst liberation of inorganic phosphate (1mol/mol myosin) in its Mg-ATPase reaction. The LINEWEAVER BURK plots of myosin ATPase activities revealed tha the Vmax values were considrably different, but the Km values remained the same, for th myosins of the two species. The profile of the ATPase activity of squid myosin against pCMB treatment was remarkably different from rabbit; no initial activation phase was observed in squid myosin. These results confirmed that the enzymatic properties of squid myosin were similar to those of rabbit myosin in many respects, although a few properties were unique to squid myosin.