Effect of rabbit light-meromyosin on filament forming ability of fish myosin and biochemical properties of their co-filament.

Myosins from tilapia, carp, and rabbit muscles, were mixed with rabbit light-meromyosin (LMM) in a medium of 0.5M KCl (pH 7.5) and KCl concentration was diluted into 0.1M to form each filament and co-filament from myosin and LMM, respectively. Thus, the effect of LMM on the ultrastructure in electron micrographs and on some biochemical properties of these filaments were investigated. In general, when the myosin formed thick filaments and co-filaments with LMM bigger size of 290A in width and 0, 72μm in length, the central bare zone was known to be formed. The actin-activation of myosin Mg-ATPase of these bipolar filaments occurred and specific activity was saturated by a small amount of actin. Moreover, such filaments and co-filaments as above were found to be hard to disassemble into mysoin and LMM (or its short fila-ments), from the change in light scattering intensity caused by treatment with KCl or ATP. In particular, thick filaments of tilapia myosin formed in vitro, can be disassembled by a relatively low concentration of KCl or ATP, and the actin-activation of its Mg-ATPase was weak. However, LMM increases in the actin-activation of myosin Mg-ATPase by forming ATP or KCl resistant bipolar co-filaments with myosin.