Discrete reduction of type I collagen thermal stability upon oxidation

The oxidation of acid-soluble calf skin collagen type I caused by metal-dep endent free radical generating systems, Fe(II)/H2O2 and Cu(II)/H2O2, was fo und to bring down in a specific, discrete way the collagen thermal stabilit y, as determined by microcalorimetry and scanning densitometry. Initial oxi dation results in splitting of the collagen denaturational transition into two components. Along with the endotherm at 41 degrees C typical for non-ox idized collagen, a second, similarly cooperative endotherm appears at 35 de grees C and increases in enthalpy with the oxidant concentration and exposu re time, while the first peak correspondingly decreases. The two transition s at 35 and 41 degrees C were registered by densitometry as stepwise increa ses of the collagen-specific volume. Further oxidation results in massive c ollagen destruction manifested as abolishment of both denaturational transi tions. The two oxidative systems used produce identical effects on the coll agen stability but at higher concentrations of Cu(II) in comparison to Fe(I I). The discrete reduction of the protein thermal stability is accompanied by a decrease of the Gee amino groups, suggestive of an oxidation attack of the side chains of lysine residues. Since the denaturation temperature of collagen shifts from above to below body temperature (41 degrees C-35 degre es C) upon oxidation, it appears important to account for this effect in a context of the possible physiological implications of collagen oxidation. ( C) 1999 Published by Elsevier Science B.V. All rights reserved.