Effect of C-protein and LC-light chains on actomyosin ATPase at various ionic strength and calcium levels.

Interrelation between the effects of C-protein and LC2-light chains on actin-activated ATPase activity of skeletal muscle myosin has been investigated at various ionic strength (0.06-0.14) and free calcium levels (10(-4) M, 10(-8) M). The ATPase activity of AM reconstituted with column-purified myosin or partly-purified myosin and non-regulated actin exhibits a pronounced dependence on ionic strength with maximum at I = 0.1. C-protein impurities (5 per cent) usually present in Minit can inhibit AM ATPase at every ionic strength assayed, without changing the character of this dependence. Actin-activated ATPase of the above myosins shows calcium sensitivity at every ionic strength studied. The partial removal of LC2 from Mcol results in a decrease of AM ATPase and in a disappearance of its calcium sensitivity. C-protein added to Mcol in a molar ratio of 1:1 inhibits considerably AM ATPase, reduces its sensitivity to ionic strength and abolishes its calcium sensitivity.