Effects of Methylxanthines on Superprecipitation of Myosin B Extracted from Rabbit Fast Skeletal Muscle

Abstract

Myosin B was extracted from rabbit fast skeletal muscle. Caffeine (2-70mM), theophylline (2-30mM), and theobromine (2mM) were examined for their effects on the rate and extent of myosin B superprecipitation at a low ionic strength (50mM KCl) and a low concentration of ATP (40 μm) by the turbidimetric method. The rate of the superprecipitation was significantly (p<0.05 and p<0.01) reduced by 30-70mM caffeine and 2-30mM theophylline, while the extent was significantly (p<0.01) increased by 10-30mM theophylline. The onset of the superprecipitation was also delayed and a clearing phase was even induced by 50-70mM caffeine. Theobromine had no significant effect on the rate or extent of the superprecipitation at the concentration used. These results indicate that caffeine and theophylline are retardants of the myosin B superprecipitation reaction in the concentration ranges investigated.