Actin from Heart Muscle: Isolation, Purification, and Physicochemical Properties

A systematic study of the preparation of actin from cardiac muscle has led to the use of a modification of Straub's original technique which gave good yields of an F-actin with very high polymerizing activity. The G-actin obtained by this method was found to be homogneous in starch gel electrophoresis; the sedimentation behavior suggested that small amounts of oligomers of G-actin may have been present in addition to monomeric G-actin, but there was no evidence of impurity. The partial specific volume of dog cardiac actin was approximately 0.715 ml/g, the sedimentation coefficient extrapolated to infinite dilution of the protein was 3.44 S, and the intrinsic viscosity was 0.16 dl/g. Precise measurement of the diffusion coefficient was not feasible due to the instability of the G-actin monomers in solutions of high ionic strength. The sedimentation behavior of rabbit cardiac actin was similar to that of dog cardiac actin. The molecular weight of dog cardiac actin, estimated from sedimentation and viscosity data, was 62, 300. Since this estimate of molecular weight is similar to published values for rabbit skeletal actin, the different properties of cardiac and skeletal muscle cannot be attributed to a major physicochemical difference between the actins of these two tissues.