摘要：

Degradation of collagen by oxidant species may play an important role in the progression of rheumatoid arthritis. Whilst the overall effects of this process are reasonably well defined, little is known about the sites of attack, the nature of the intermediates, or the mechanism(s) of degradation. In this study electron paramagnetic resonance spectroscopy with spin trapping has been used to identify radicals formed on collagen and related materials by metal ion — H 2 O 2 mixtures. Attack of the hydroxyl radical, from a Fe(II)-H 2 O 2 redox couple, on collagen peptides gave signals from both side chain ( . CHR′R′'), and α-carbon [ . C(R)(NH -)CO -, R = side-chain] radicals. Reaction with collagen gave both broad anisotropic signals, from high-molecular-weight protein-derived radicals, and isotropic signals from mobile species. The latter may be low-molecular-weight fragments, or mobile side-chain species; these signals are similar to those from the α-carbon site of peptides and the side-chain of lysine. Enzymatic digestion of the large, protein-derived, species;releases similar low-molecular-weight adducts. The metal ion employed has a dramatic effect on the species observed. With Cu(I)-H 2 O 2 or Cu(II)-H 2 O 2 instead of Fe(II)-H 2 O 2 , evidence has been obtained for: i) altered sites of attack and fragmentation, ii) C-terminal decarboxylation, and iii) hydrogen abstraction at N-terminal α-carbon sites. This altered behaviour is believed to be due to the binding of copper ions to some substrates and hence site-specific damage. This has been confirmed in some cases by electron paramagnetic resonance studies of the Cu(II) ions.

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