Differences in the energetics of collagen denaturation in connective tissue from two muscles

The thermal denaturation of collagen the perimysium of intramuscular connective tissue isolated from bovine Semitendinosus (ST) and Perctoralis profundus (PP) muscles was investigated using a range of heating rates in differential scanning calorimetry (DSC) and analyzed by application of the Kissinger-Akahira-Sunose (KAS) and Lumry-Eyring models. Thermograms showed a broadening of endotherms and a shift towards higher temperatures as the thermal scanning rate increased. These features are consistent with the two-step process of a reversible transition between native and unfolded collagen molecules followed by an irreversible transition between unfolded and denatured states. There were small differences between muscles in the onset temperatures of the thermal transitions at heating rates of 0.5 K min^-1, while both the KAS and Lumry-Eyring models yielded similar values for the effective activation energy of the whole two-step process, the Lumry-Eyring model allowed a greater insight into differences in the reversible and irreversible steps between the perimysium both muscles. Reversible unwinding of the triple-helical collagen molecules in the perimysium from ST muscle required more energy than in PP muscle. It is speculated that the presence of large amounts of elastin in the perimysium of ST muscles may influence this due to a protein crowding mechanism, or by affecting the covalent cross-linking of the collagen.