I~elaxation in Extracted Muscle Fibers* by Emil Bozler

Szent Gy~rgyi (1-3) discovered that ATP 1 produces a strong contraction in muscle fibers which have been preserved in glycerol. Later Bozler (4-7) found that such fibers, which originally are in rigor, can be transformed into a state closely resembling normal relaxation by physiological concentrations of ATP. The fibers then are very extensible and plastic, and give a strong contraction on addition of smal_l amounts of CaCIs. This state can be produced and maintained only in the presence of Mg and only in rather fresh fibers. Following up work by Marsh (8) on the syneresis of muscle homogenates, Bendall (9) has shown that the ability of briefly extracted fibers to relax is due to the presence of a non-dialyzable factor contained in muscle extract, which will be called relaxation factor ("Marsh factor"). The relaxing effect of ATP is further supported by two other substances normally occurring in tissues, PC (10-12) and PP (7, 13, 14). In the present paper the clarification of the mechanism of action of these factors will be attempted, particularly that of the relaxation factor. I t was found that EDTA closely imitates all the effects of this factor. The results indicate that relaxation is caused by the inactivation of bound Ca. Previous evidence that the relaxed state is due to the formation of an enzymatically inactive ATP-protein complex was confirmed.