Inhibitory Actions of Synthetic Actin Peptides and 2,3-Butanedion Monoxime on Actomyosin System

Interaction of myosin and actin has been studied in the presence of inhibitors in order to identify and characterize sites essential for the motor function. Acidic amino acid cluster of actin at the amino terminal region is known to interact with basic residue around 50K-20K connecting loop of the myosin heavy chain. In this study, an amino terminal peptide region of actin without the initial four acidic residue cluster is also shown to have important role in the interaction with myosin in the presence of ATP. A set of peptides corresponding to actin sequences from Leu8 to Arg28 or to Gly36 were synthesized. In the absence of actin, neither activation nor inhibition of MgATPase activity of S1 alone has been observed with both types of peptide. In the presence of actin, however, the longer peptide (L8G36) at 50 μM shows about 50% inactivation of the control value of actoS1 Mg2+ATPase activity. The shorter one (L8R28) has been a non competitive and weaker inhibitor. The inhibition could be interpreted as a results of impairing of one of the interactions necessary for normal progression of actomyosin ATPase reaction. Moreover, these results indicate a contribution of amino terminal sequence of actin without initial four acidic residues for the acto myosin interaction. Examination of the inhibitory mechanism of BDM has shown that the effect may not be due to lowering the binding affinity between actin and myosin.