Effect of temperature on Mg-ITP-induced superprecipitation of actomyosin.

Superprecipitation of an actomyosin suspension was measured at various temperatures (2.5 degrees - 20 degrees) using Mg-ITP as substrate. Superprecipitation was induced by the addition of Mg-ITP at all temperatures, but decreased in extent with decrease in temperature. The predominant intermediate in the Mg-ITP hydrolysis of myosin depends on the temperature; at 20 degrees it is the myosin-IDP-Pi complex, while below 8 degrees it is the myosin-ITP complex (Hozumi, T. (1976) Eur. J. Biochem. 63, 241). Therefore, the occurrence of superprecipitation below 8 degrees is not compatible with muscle models in which formation of a myosin-product complex is the rate-limiting intermediate.