Effects of ultraviolet irradiation on native and telopeptide-poor collagen

Abstract

Effects of ultraviolet light on physical, chemical and immunologic properties of acid-soluble and enzyme (proctase)-treated collagen were studied. Ultraviolet irradiation in air caused an initial increase in viscosity of both collagen preparations, rapidly followed by a loss of viscosity and a loss of negative optical rotation. Ultraviolet irradiation in nitrogen, however, led to a rapid increase in viscosity until a gel formed. With prolonged irradiation, this gel also depolymerized. Enzyme-treated collagen was less sensitive to the effects of ultraviolet irradiation than was acid-soluble collagen. Immunologic reactivity of enzyme-treated collagen was rapidly lost with short exposures to ultraviolet irradiation. Ultraviolet irradiation also inhibited fiber formation. These results suggest that photochemical modifications occur at telopeptide regions or remaining aromatic residues of enzyme-treated collagen during early stages of irradiation. The transition temperature of the melting curve of collagen became broad but there was no loss of negative optical rotation, suggesting that scission of collagen molecules into shorter fragments which retain helical configurations occurred with longer periods of irradiation. Splitting of the polypeptide chain probably occurs between nitrogen and the α-carbon.