A kinetic model for the molecular basis of the contractile activity of Acanthamoeba myosins IA and IB.

摘要: Acanthamoeba myosins IA and IB are single-headed, monomeric molecules consisting of one heavy chain light chain. Both have high actin-activated Mg2+-ATPase activity, when the is phosphorylated, but neither seems to be able form bipolar filaments that generally thought required for actomyosin-dependent contractility. In this paper, we show that, at fixed F-actin concentration, activities increase about 5-fold in specific activity a cooperative manner as myosin concentration increased. The range over which change occurs depends on actin concentration. More I concentrations F-actin. limiting caused by decrease KATPase low states same Vmax infinite completely bound long before values reached. Therefore, much activation must result interactions between actomyosin. These kinetic data can explained model shift from state results cross-linking I. Cross-linking might occur either through two actin-binding sites single molecule or dimers oligomers induced interaction monomers with filaments. ability cross-link demonstrated accompanying paper (Fujisaki, H., Albanesi, J.P., Korn, E.D. (1985) J. Biol. Chem. 260, 11183-11189).