Structural properties of frog muscle myosin.

Frog myosin is a labile molecule, undergoing irreversible aggregation and rapid loss of ATPase; however, a procedure is described which provides highly purified myosin, with stable solubility and enzymatic properties, from skeletal muscle of Rana catesbeiana. Frog myosin contains heavy chains and light chains 1, 2, and 3. Light chain 3 is present in excess over light chain 1, and light chain 2 may occur as either, or both, of 2 closely migrating bands. On two-dimensional electrophoresis, light chain 1 generates an isoelectric component with pK 5.60; light chain 2 generates a complex pattern with 3 or 4 major components; and light chain 3 generates 2 major components with pK 5.00 and 4.92. The same subunit composition is obtained for frogs acclimated at 25 and 5 degrees C; however, proteolytic artifacts may occur in myosin preparations purified in the absence of protease inhibitors, especially in warm-acclimated frogs.