title: Changes in molar volume and heat capacity of actin upon polymerization.
abstract: We have used densimetry and microcalorimetry to measure the changes in molar volume and heat capacity of the actin molecule during Mg(2+)-induced polymerization. Molar volume is decreased by 720 ml/mol. This result is in contradiction with previous measurements by Ikkai and Ooi [(1966) Science 152, 1756-1757], and by Swezey and Somero [(1985) Biochemistry 24, 852-860]: both of these groups reported increases in actin volume during polymerization, of 391 ml/mol and 63 ml/mol respectively. We also observed a decrease in heat capacity of about 69.5 kJ.K-1.mol-1 during polymerization. This is in agreement with the concept of conformational fluctuation of proteins proposed by Lumry and Gregory [(1989) J.Mol. Liq. 42, 113-144]whereby either ligand binding by a protein or monomer-monomer interaction decreases the protein's conformational flexibility.
authors.affiliation: INRS-Energie et matériaux, Varennes, P.Q., Canada.
authors.forename: F
authors.initials: F
authors.lastname: Quirion
authors.forename: C
authors.initials: C
authors.lastname: Gicquaud
mesh_terms: D000199:Actins / Q000737:chemistry*; D000818:Animals; D002151:Calorimetry; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D046911:Macromolecular Substances; D008274:Magnesium / Q000494:pharmacology; D015636:Magnesium Chloride / Q000494:pharmacology; D011108:Polymers / Q000737:chemistry*; D011487:Protein Conformation; D011817:Rabbits; D013816:Thermodynamics
chemical_list: D000199:Actins; D046911:Macromolecular Substances; D011108:Polymers; D015636:Magnesium Chloride; D008274:Magnesium