title: Regulation of the actin-activated ATPase activity of Acanthamoeba myosin I by cross-linking actin filaments.
abstract: The actin-activated Mg2+-ATPase activity of phosphorylated Acanthamoeba myosin I was previously shown to be cooperatively dependent on the myosin concentration (Albanesi, J. P., Fujisaki, H., and Korn, E. D. (1985) J. Biol. Chem. 260, 11174-11179). This observation was rationalized by assuming that myosin I contains a high-affinity and a low-affinity F-actin-binding site and that binding at the low-affinity site is responsible for the actin-activated ATPase activity. Therefore, enzymatic activity would correlate with the cross-linking of actin filaments by myosin I, and the cooperative increase in specific activity at high myosin:actin ratios would result from the fact that cross-linking by one myosin molecule would increase the effective F-actin concentration for neighboring myosin molecules. This model predicts that high specific activity should occur at myosin:actin ratios below that required for cooperative interactions if the actin filaments are cross-linked by catalytically inert cross-linking proteins. This prediction has been confirmed by cross-linking actin filaments with either of three gelation factors isolated from Acanthamoeba, one of which has not been previously described, or by enzymatically inactive unphosphorylated Acanthamoeba myosin I.
mesh_terms: D000199:Actins / Q000378:metabolism / Q000494:pharmacology*; D000205:Actomyosin / Q000378:metabolism; D000656:Amoeba / Q000032:analysis*; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D002352:Carrier Proteins; D003432:Cross-Linking Reagents / Q000494:pharmacology; D008840:Microfilament Proteins / Q000494:pharmacology; D009218:Myosins / Q000378:metabolism* / Q000494:pharmacology; D010766:Phosphorylation
chemical_list: D000199:Actins; D002352:Carrier Proteins; D003432:Cross-Linking Reagents; C034037:F-actin-binding proteins; D008840:Microfilament Proteins; D000205:Actomyosin; D017301:Ca(2+) Mg(2+)-ATPase; D009218:Myosins