Denaturation of Collagen Fibers in Nai, NaCL and Water of Different pH Values as Studied by Differential Scanning Calorimetric Measurements

Microcalorimetric measurements of rat tail tendon collagen in different aqueous media show the following behavior of denaturation temperature (Td) and of denaturation enthalpy (ΔHd): H+ and OH− ions lower Td significantly beyond pH 4... 11. Addition of salts (0.15 M) generally lowers Td in the range between pH 5 and 10, I− being more effective than C1− at pH > i.p. However, in the region of pH < i.p., I− raises Td to values above those of Cl− and even those of water. The value of ΔHd was found to be insensitive to pH over the pH range of 4... 11. Hence the lowering of Td is assumed firstly to be due to a (ionic) disorganization of the water contacting the polypeptide chains and secondly to their mutual electrostatic repulsion. The appearance of ΔHd is thought mainly to be due to a rupture of interchain bonds.