The Fast-Reacting Lysine Residues of F-actin We modified the fast-reactive lysine residues of F-actin with maleic anhydride and investigated the interaction of the modified F-actin with myosin. The results are as fellows, 1,After F-actin solution was treated with maleic anhydride, the resulting F-actin ("Maleyl F-actin") was isolated from the reaction mixture by high-speed centrifugation. The "Maleyl F-actin" obtained was maleylated to the extent of only 1 or 2 moles of lysine per mole of

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... The amount of "Maleyl F-actin" decreased with increasing concentration of maleic anhydride in the reaction mixture. The viscosity of "Maleyl Factin" was lower than that of unmodified F-actin. 2.The rate and degree of syneresis of actomyosin superprecipitated from "Maleyl Factin" were higher than those of actomyosin from unmodified F-actin. 3. The activity of myosin ATPase induced by "Maleyl F-actin" was markedly higher than that of actomyosin ATPase from unmodified F-actin. This peculiar activation of the myosin ATPase induced by "Maleyl F-actin" was decreased by chemical modification of the special SH1 residue (SH1) in the myosin molecule with N-ethylmaleimide. These results suggest that the conformation of "Maleyl F-actin" is different from that of unmodified F-actin, inducing a change in viscosity. Therefore, in contrast to unmodified F-actin, "Maleyl F-actin" might combine tightly with the SH, region of the myosin molecule to increase myosin ATPase activity markedly.