Transition temperature and enthalpy change dependence on stabilizing and destabilizing ions in the helix–coil transition in native tendon collagen

Abstract

SynopsisThe transition temperatures t( and enthalpy changes AH in the helix-coil transition of' solid tendon collagen soaked in a solution containing one of the following stabilizing o r destabilizing agents, HCHO, NaF, NaCI, NaI, NaBr, NaOH, NH2CONH2, CaCI?, MgCIz, were measured as a function of molar concentration by a calorimetric method. The temperature and the enthalpy changes accompanying the transition behaved in a similar manner: when the t l was depressed by the presence of ions, similar behavior was observed in M. Both parameters ( 1 , and A H ) increased for HCHO, and decreased for NaF and NaCl a t concentrations lower than 0.2 M. Above 0.2 M they increased for NaF and NaCI, and decreased in the presence of' the other reagents listed above. T h e average t( and the AH observed in collagen soaked in water were 635°C and 12.3 calig, respectively. In addition to the parameters mentioned above, the molar effectiveness of the various reagents was obtained for the cases where there was a linear relationship between the tf and molar concentration of the reagent in the solution.Since both the ti and the AH were observed to vary, the entropy change ( A S ) accompanying the transition was calculated using thermodynamic relations. In order to explain the A.9 observed a s a function of ionic concentration, the thermodynamic relationships have been obtained from a partition function under suitable assumptions. Since the partition function is dependent on the number of hydrogen bonds responsible for collagen stability, the result obtained has been compared with the values predicted by the two most quoted models for collagen. T h e present study is in accordance with the Ramachandran model for collagen structure, which predicts more than one hydrogen bond per three residues.

Influence of Sodium, Potassium and Magnesium Chloride on Thermal Properties of Beef Muscle

“…On the other hand MgClz affected muscle protein denaturation in a different way than either NaCl or KC1 (Table 1). This effect was certainly due to the divalent cation (Mg+ +) as was also indicated by Lim (1976) and Starbursvik and Martens (1980). The shape of the curve shadowed the 5% NaCl profile.…”

Heat‐induced contraction of blood vessels

“…Upon shrinkage, the contractile elements must act against an existing force and therefore exert work. Shrinkage of collagen fibers during denaturation has been proposed to be represented by a first-order phase transition [17], including the exchange of latent heat [21]. A modified Clausius-Clapeyron equation can be derived that describes the constrictive force, which depends on the molar weight of collagen and its latent heat of denaturation versus the temperature excess above T,.…”

The Increase in Denaturation Temperature Following Cross-linking of Collagen is Caused by Dehydration of the Fibres

“…Ions affect the denaturation temperature of collagen in solution 22 and in fibres 23 and the effect depends on ion concentration and on the identity of the ions involved. 24 Thus, a particular salt solution at a particular pH value may have a stabilizing or a destabilizing effect on the molecule itself, and it may swell or shrink the fibre. The results of these studies indicate that analysis of the temperature stability of fibres would be clarified by separating the effects of confinement of the molecule in the fibre lattice from the intrinsic effects on the molecule itself.…”