Type I collagen segment long spacing banding patterns. Evidence that the alpha 2 chain is in the reference or A position.

Densitometric scans of electron micrographs of type I collagen segment long spacing crystallites stained with uranyl acetate or phosphotungstic acid and uranyl acetate have been correlated with computer-synthesized scans derived from the sequence of the alpha 1(I) and alpha 2 chains. Three models that differ in the location of the alpha 2 chain were used in the computer synthesis; Models A, B, and C have the alpha 2 chain in the A, B, and C chain positions, respectively. For all 13 experimental scans, the order of decreasing correlation with the models was found to be A,B,C. The probability of getting the same order of decreasing correlation all 13 times is 6/6(13). It was also determined at the 0.99 confidence level that the mean of the differences in the correlation coefficients among the models is greater than 0, supporting the conclusion that sequence-derived models best fit the experimental data when the alpha 2 chain is in the A position. Our results also agree with recent studies that show that uranyl ions bind to both positively and negatively charged residues on collagen type I.