The chemical composition of bovine vitreous-humour collagen fibres

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Abstract
The insoluble protein fraction was prepared from the central and posterior peripheral fraction of bovine vitreous humor. 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-humor collagen .alpha.-chains differed from those of cartilage collagen in that they had a lower Ala content and differed in their susceptibility to cleavage by CNBr. Satisfactory cleavage was obtained after 2 CNBr treatments involving reduction and alkylation. Significant quantities of other peptide constituents were present in the vitreous-humor 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-humor collagen preparations is not known, 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-humor collagen indicate that vitreous-humor fibers are composed of a special type-II collagen.