THE CONTRACTION AND EXTRACTION CHARACTERISTICS OF CONTRACTILE PROTEINS FROM IN VIVO RYANODINE-RIGORED AND IODOACETIC ACID-RIGORED SKELETAL MUSCLE

¹ Department of Pharmacology, State University of New York, Downstate Medical Center, Brooklyn, N.Y.

The contractile properties of model fibers prepared from skeletal muscle proteins obtained from in vivo ryanodine-rigored rabbits (myosin-R), iodoacetaterigored rabbits (myosin-I) and pentobarbital-anesthetized rabbits (myosin-B) were studied. On exposure to adenosine triphosphate (ATP), the fibers prepared from myosin-R developed greater tensions, milligram for milligram of protein, than did fibers prepared from either myosin-I or myosin-B. Data obtained by differential extraction of the muscle and from viscometric and electrophoretic analyses of the proteins support the conclusion that myosin-R is probably a total preparation of actomyosin. It is this which accounts for the observed superior contractile properties of myosin-R fibers as compared to the contractile properties of fibers prepared from either myosin-I or myosin-B. The extraction and viscometric and electrophoretic data obtained with myosin-I suggest that it is probably myosin-B, or closely related to it. It bears no relation to the -myosin of Dubuisson.