Temperature Dependence Of Dissociation Research Articles

Thermodynamics and temperature dependence of dissociation and solvation of alpha-alanine in H 2O-MeOH and of valine in H 2O-PrOH-2

Thermodynamic constants of amino acid dissociation with carboxylic, K 1, and amino groups, K 2, and standard thermodynamic functions of dissociation (Δ G 0 d,1, Δ G 0 d,2, Δ H 0 d,1, Δ H 0 d,2, Δ S 0 d,1, Δ S 0 d,2) of α-alanine in methanol–water solvent and of valine in propan-2-ol-water solvent (0, 20, 40, 60, 80 wt.%) have been determined by potentiometric method in galvanic cells without liquid junction at 278.15–328.15 K (with step of 10 K). The standard Gibbs energy of transfer of ionic forms of α-amino acids in MeOH-H 2O, PrOH-2-H 2O mixtures have been calculated. The short-range interaction part of dissociation Gibbs energy, Δ G 0 d,1,2 ⁎ have been obtained assuming the borders of ionic association area.

Effects of Two Familial Hypertrophic Cardiomyopathy Mutations in α-Tropomyosin, Asp175Asn and Glu180Gly, on the Thermal Unfolding of Actin-Bound Tropomyosin

Differential scanning calorimetry was used to investigate the thermal unfolding of native α-tropomyosin (Tm), wild-type α-Tm expressed in Escherichia coli and the wild-type α-Tm carrying either of two missense mutations associated with familial hypertrophic cardiomyopathy, D175N or E180G. Recombinant α-Tm was expressed with an N-terminal Ala-Ser extension to substitute for the essential N-terminal acetylation of the native Tm. Native and Ala-Ser-Tm were indistinguishable in our assays. In the absence of F-actin, the thermal unfolding of Tm was reversible and the heat sorption curve of Tm with Cys-190 reduced was decomposed into two separate calorimetric domains with maxima at ∼42 and 51°C. In the presence of phalloidin-stabilized F-actin, a new cooperative transition appears at 46–47°C and completely disappears after the irreversible denaturation of F-actin. A good correlation was found to exist between the maximum of this peak and the temperature of half-maximal dissociation of the F-actin/Tm complex as determined by light scattering experiments. We conclude that Tm thermal denaturation only occurs upon its dissociation from F-actin. In the presence of F-actin, D175N α-Tm shows a melting profile and temperature dependence of dissociation from F-actin similar to those for wild-type α-Tm. The actin-induced stabilization of E180G α-Tm is significantly less than for wild-type α-Tm and D175N α-Tm, and this property could contribute to the more severe myopathy phenotype reported for this mutation.