ON FORMATION AND STABILITY OF ENZYMICALLY ACTIVE COMPLEXES OF HEAVY MEROMYOSIN WITH ACTIN

The increase in enzymic activity, obtained upon addition of excess F-actin to one mole of heavy meromyosin, equals that obtained upon addition of a concentrated solution of heavy meromyosin to one mole of G-actin monomeric units (in the form of F-actin). It is concluded that the molar ratio of heavy meromyosin to G-actin in the resulting enzymically active complex is one to one. Two actin preparations suggested the formation of a 1:2 active complex in addition to the 1:1. Probably both subfragment-1 units of heavy meromyosin can bind to G-actin units in the F-actin filaments, both being activated to the same extent. The values of the apparent association constants for the reactions resulting in the formation of the two types of complexes and of the kinetic constant for the subsequent reactions resulting in ATP hydrolysis are determined. The same type of analysis is applied to other authors' data. The stochiometry of myosin to actin binding in actomyosin, and possible applications to muscle contraction are discussed. © 1969.