Comparison of intermonomer interactions within polymers of chicken gizzard and rabbit skeletal muscle actins

Comparison of interactions between the monomers of chicken gizzard and skeletal muscle actin revealed: 1. A more pronounced increase of the extent of polymerization of chicken gizzard than skeletal muscle actin with temperature, which resulted in higher positive changes of entropy and enthalpy of the former than of the latter species. 2. A difference in spectral changes accompanying polymerization: the changes at 295 nm, attibuted to environmental changes around tryptophan residues, were less pronounced for gizzard than for skeletal actin. 3. A difference in the amount of heavy meromyosin added to gizzard and to skeletal F-actin, with which the degree of flow birefringence of the acto-HMM complex is minimum: this amount was lower in the former than in the latter case. These results indicate quantitative differences between intermonomer interactions involved in polymerization of both actin species and also a possible difference in cooperativity between the monomers within the polymers of gizzard and skeletal actin.