Cross-linking in Collagen by Potassium Nitrosyldisulphonate

Abstract

Earland and Stell^1,2 found that wool, silk, casein and insulin, when treated with potassium nitrosyl disulphonate (KNDS), acquired altered properties which led them to conclude that new interchain cross-links had been formed and that tyrosine residues were involved in their formation. The tyrosine was first converted by a sequence of oxidative stages to reactive indole 5 : 6 quinones, which could then cross-link with suitably positioned side chains, for example, with another indolequinone residue to form a melanin type dimer or with an amino group to form an amino-substituted 5 : 6 dihydroxy indole¹. Tryptophan, free or bound, is also oxidized by KNDS and the disulphide group of cystine is slowly oxidized to sulphonic acid². We have found that the other natural α-amino-acids are resistant to KNDS, and because collagen is virtually free from cystine and tryptophan it seemed to be interesting to examine the effects of KNDS on this protein, for its action would be specifically directed towards its tyrosine residues. Other oxidative procedures, for example, ultraviolet light irradiation, are less specific.