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Oxazolidine E, an aldehydic cross-linking agent, is used to impart hydrothermal stability to collagen. The purpose of this study was to investigate the exact nature of oxazolidine E induced cross-links with collagen by using synthetic peptides having sequence homology with collagen type I. Tandem mass spectrometry revealed the formation of methylol and Schiff-base adducts upon reaction of oxazolidine E with the peptides. This was confirmed by allowing the reaction to proceed under reducing conditions using cyanoborohydride. Mass spectrometry (MS)-MS analysis clearly showed interaction of tryptophan and lysine residues with oxazolidine E and demonstrated that arginine could be cross-linked with glycine in the presence of oxazolidine E through the formation of a methylene bridge. Collagen fibrils regenerated from monomers in the presence and absence of oxazolidine E were studied using atomic force microscopy to investigate morphological alterations. Regenerated fibrils showing the typical 65 nm D-banding pattern were obtained from those formed both in the presence and absence of oxazolidine E, and there was no evidence of a change in the D-periodicity of these fibrils. This indicated that oxazolidine E does not hinder collagen molecules from correctly aligning to form the quarter-stagger structure.

It is necessary to understand the changes that occur during the initial processing of lamb skins, because these will affect the final quality of the leather. The types of collagen, their macro and micro structures, the presence of proteins other than collagens, and the quantity and the type of proteoglycans, all have a profound effect on the quality of leather. Proteins isolated from untreated or raw sheep skin and from pickled skin (skins treated with sodium sulfide and lime followed by bating with enzymes, then preserved in sodium chloride and sulfuric acid) were significantly different when analysed by use of 2D gel electrophoresis and mass spectrometry. Agarose gel electrophoresis with a very sensitive sequential staining procedure has been used to identify the glycosaminoglycans present in raw and treated skin and their impact on quality of leather. Results showed that effective removal of proteoglycans acting as inter-fibrillar adhesives of collagen fibrils seemed to improve leather quality. Removal of these molecules not only opens up the fibre structure of the skin but may also be important in wool removal. The presence of elastin, which imparts elastic properties to skin, is of significant importance to tanners. The amino acids desmosine and isodesmosine, found exclusively in elastin, were quantitatively analysed to assess the role of elastin in leather quality.

The effects of conventional lime sulfide depilation and enzymatic depilation on the enamel layer of pickled lamb pelts were examined using atomic force and optical microscopy, immunohistological, and proteomic techniques. Microscopy showed that the surface structure of enzymatically depilated material was visibly less organized than conventionally processed material, implying that the enzymes used for depilation were responsible for this difference. Proteomic analyses identified an absence of collagen VI in the enamel of skins that had been processed with enzymes, in contrast to the skins that had been processed using conventional methods, which was confirmed using immunolocalization studies. It is therefore possible that the destruction of collagen VI during enzymatic depilation may cause the changes to the enamel structure observed during enzyme processing and in turn affect the quality of the finished product.