Type I collagen segment long spacing banding patterns: Improved correlation with models using a variable h‐spacing

Five models of collagen molecular structure incorporating a variable h‐spacing were evaluated by comparing theoretical densitometric scans of segment long spacing (SLS) banding patterns with experimental densitometric scans. The five models tested assumed a shift in the h‐spacing of different residues: (1) proline only, (2) hydroxyproline only, (3) proline and hydroxyproline (in the same direction), (4) proline and hydroxyproline (in opposite directions), and (5) all residues shifted depending on their relative hydrophobicity. The best correlation coefficients were obtained when, in the theoretical models, the proline residues were expanded axially and/or the hydroxyproline residues were contracted. Using the hydrophobic model, the results showed that in general the more hydrophobic a residue is, the larger its h‐spacing. Theorectical models with the α2‐chain in the A position of the triple helix (α2,α1,α1) correlated best with the experimental data. In conclusion, these studies suggest that variation exists in the h‐spacing of the amino acid residues proline and hydroxyproline in SLS prepared for electron microscopy and stained with phosphotungstic acid and uranyl acetate. Some of this variation may be due to drying and may not be present in hydrated molecules.