Cartilage type II collagen fibrils show distinctive negative-staining band patterns differences between type II and type I unfixed or glutaraldehyde-fixed collagen fibrils

Abstract

The cross striation of native and reconstituted collagen fibrils is believed to conform to a unique D-band pattern independently of the genetically distinct types of fibril-forming collagens. This investigation focuses on type II native collagen fibrils, whose negative-staining patterns are shown to differ from the usual banding exhibited by type I collagen fibrils. Negative staining with phosphotungstic acid, pH 7.4, was carried out on a) unfixed and b) glutaraldehyde-fixed collagen fibrils isolated from bovine hyaline cartilages. The band patterns obtained and their microdensitograms were compared to similarly processed type I collagen fibrils isolated from bovine fibrous tissues. Only minor differences were observed in unfixed fibrils. In the intraperiod light zones of type II fibrils, two dark bands (interbands X2-Y4 and Y4-Y2) showed different intensities with respect to their homologous bands in type I fibrils. In contrast, a marked difference was shown by glutaraldehyde-fixed fibrils. In comparison with type I fibrils, the greater stain exclusion capacity of type II fibrils yielded both the appearance of supernumerary bands, which altered banding in two intraperiod regions, and differences in the intensity of several bands in three intraperiod regions where the band distribution was similar. This stain exclusion pattern may be accounted for by molecular extradensity. The possibility that it depends on linkage with a higher number of glutaraldehyde residues and/or the persistence of cross-linked collagenic or non-collagenic proteins is discussed. To refer to the glutaraldehyde-induced band patterns in negatively stained type II and type I collagen fibrils, the terms "bands GA(II) 1-12" and "bands GA(I) 1-15," respectively, are proposed.