Effect of Actomyosin on Heat-induced Gelation of Myosin

Abstract

Myosin and reconstituted actomyosin free of regulatory proteins were mixed in 0.6 m kc1 and 20 mM phosphate buffer at pH 6.0 and were tested quantitatively for thermally induced gelation properties by measuring the rigidity of the system at 65°C. Full enhancement of gelation was attained when the weight ratio of myosin-to-actomyosin was about 4. The addition of regulatory proteins to actomyosin could restore calcium sensitivity of the contractile system, but did not affect the heat-induced gelation of myosin in the presence of actomyosin, suggesting that regulatory proteins play no role in the heat-induced gelation of the system. Neither the single and double headed subfragments, both capable of interacting with F-actin, nor the helical tail subfragments, devoid of the intracting site with F-actin, exhibited changes in thermogelling properties when mixed with F-actin. However, upon addition to F-actomyosin, the tail subfragments revealed a significant effect on the gelation of actomyosin, whereas the headed subfragments exerted no influence over gelation of the system. These results indicate that the enhancing effect of F-actin on the heat-induced gelation of myosin was brought about solely by the limited amount of F-actomyosin formed in the system, which acts as a cross-linker between the tail portion of bound and free myosin molecules. © 1982, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.