title: Thermodynamics of actin polymerization; influence of the tightly bound divalent cation and nucleotide.
abstract: Previous work by this laboratory has shown that the tightly bound divalent cation of actin affects the enthalpy of the polymerization reaction for ATP-actin (Selden et al. (1986) J. Muscle Res. Cell Motil. 7, 215-224). In the present study, we have measured the temperature dependence of polymerization for actin containing ATP or ADP as the bound nucleotide and Mg2+ or Ca2+ (Mg-actin or Ca-actin) as the tightly bound divalent cation. In contrast to the marked effect of the tightly bound divalent cation on enthalpy and entropy changes for the polymerization of ATP-actin, ADP-actin polymerization is affected very little by the tightly bound divalent cation. The Arrhenius and van't Hoff plots for polymerization of Ca-ATP-, Mg-ADP- and Ca-ADP-actin were found to be non-linear. The free energy data for actin polymerization have been analyzed as a second order function of absolute temperature (Osborne et al. (1976) Biochemistry 15, 317-320). The values of the enthalpy change and activation enthalpy change for Ca-ATP-, Mg-ADP- and Ca-ADP-actin polymerization were found to be temperature-dependent, in contrast to those for Mg-ATP-actin, which were nearly constant over the temperature range studied. These results suggest that (1) polymerization of actin which does not contain both Mg2+ and ATP may be a multi-step reaction including a rate-limiting step and (2) Mg-ATP-actin has a unique conformation which enhances its ability to polymerize.
authors.affiliation: Department of Physiology and Cell Biology, Albany Medical College, NY.
authors.forename: H J
authors.initials: HJ
authors.lastname: Kinosian
authors.forename: L A
authors.initials: LA
authors.lastname: Selden
authors.forename: J E
authors.initials: JE
authors.lastname: Estes
authors.forename: L C
authors.initials: LC
authors.lastname: Gershman
mesh_terms: D000199:Actins / Q000737:chemistry*; D000244:Adenosine Diphosphate / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000737:chemistry; D002118:Calcium / Q000737:chemistry; D002413:Cations, Divalent / Q000737:chemistry*; D005454:Fluorescence Polarization; D008274:Magnesium / Q000737:chemistry; D009711:Nucleotides / Q000737:chemistry*; D011108:Polymers; D013696:Temperature; D013816:Thermodynamics
chemical_list: D000199:Actins; D002413:Cations, Divalent; D009711:Nucleotides; D011108:Polymers; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D008274:Magnesium; D002118:Calcium