Changes induced by ozone and ultraviolet light in type I collagen. Bovine Achilles tendon collagen versus rat tail tendon collagen

Abstract

High‐molecular‐mass aggregates were made soluble from insoluble collagens of bovine Achilles tendon and rat tail tendon by limited thermal hydrolysis. These polymeric collagen aggregates were cross‐linked by 390‐nm‐fluorescent 3‐hydroxy‐pyridinium residues (excited at 325 nm) in the former tendon and by unknown non‐fluorescent residues in the latter. With the solubilized insoluble‐collagens from both tendons, as well as with acidsoluble collegen from rat tail tendon, other 350–385‐nm fluorescence intensities (excited at 300 nm) were found to be higher in monomeric hains than in dimeric and polymeric chains. Low levels of ozone inhibited fibril formation of acid‐soluble collagen particularly from young rat tail tendon, recting with tyrosine residues and the 350–385‐nm fluorophores. Aldehyde groups, involved in cross‐linking, were not effectively modified by ozone. β‐Components (α‐chain dimers) were not efficiently dissociated even by higher doses of ozone compared to γ‐components (α‐chain trimers). Polymeric chain aggregates from bovine Achilles tendon collagen, whose 3‐hydroxy‐pyridinium cross‐links are cleaved by ozone, were more readily dissociated by ozone than those from rat tail tendon collagen. Ultraviolet (300‐nm) light, which destroyed the 350–385‐nm fluorophores, inhibited fibril formation less effectively than ultraviolet (275‐nm) light, which is absorbed by tyrosine residues, and did not dissociate collagen polymers from rat tail tendon. On the other hand, ultraviolet (320‐nm) light, absorbed by 3‐hydroxy‐pyridinium cross‐links which were repidly photolyzed, partially dissociated polymeric collagen aggregates from bovine Achilles tendon after subsequent heating.