The chemical composition of bovine vitreous-humour collagen fibres

The insoluble protein fraction was prepared from the central and posterior peripheral fraction of bovine vitreous humour. The collagen present in this fraction was solubilized by pepsin and fractionated by gel chromatography. Analysis of the solubilized collagen fractions showed that the alpha-chain component had an amino acid composition and yielded a series of CNBr-cleavage peptides that showed it was very similar to type II collagen obtained from articular cartilage. Bovine vitreous-humour collagen alpha-chains differed, however, from those of cartilage collagen in that they had a lower alanine content and differed in their susceptibility to cleavage by CNBr. Satisfactory cleavage was obtained after two CNBr treatments involving reduction and alkylation. In addition, significant quantities of other peptides constituents were present in the vitreous-humour collagen fractions, and the galactose and glucose content of the alpha-chain fraction was more than double that of the same fraction obtained from articular cartilage. Although the origin of the additional peptide constituents in the vitreous-humour collagen preparations is not known, the results obtained indicate that they are probably not derived from a distinct type of alpha-chain component but may be terminal peptides covalently linked to the alpha 1 type-II helical portions of the collagen. The differences in the chemical composition of the vitreous-humour collagen indicate that vitreous-humour fibres are composed of a special type-II collagen.