Correlation between amino acid composition and ultrastructural features of type I and type II native collagen fibrils

The D-band patterns of native collagen fibrils negatively stained with phosphotungstic acid (PTA) of type II (bovine cartilaginous nasal septum) and type I (bovine reticular dermis) were compared in order to find differences and correlate these with the different amino acid composition of these two collagen types. By analyzing the averaged microdensitograms of the two types of D-banding, differences in type II fibrils were observed: a) the overlap zone was more electron-transparent on average; b) there was a different hierarchy of positive peaks (intraperiod dark bands) b1, b2 and c1; c) a more marked negative peak (intraperiod light band X3) corresponded to the C-terminal extrahelical region; d) there was a different D-location of one negative peak (intraperiod light band Y3). At the same time, different values were calculated for type I and type II tropocollagen molecule total amino acid "bulkiness" (molecular volume/length ratio) and "hydrophobicity", on the basis of literature-reported data. Consistency was found between these values and the differences of the two types of D-banding. The assumption of a correlation between the above two amino acid parameters and negative staining band patterns was supported.