Molecular structure of collagen in solution: comparison of types I,II, III and V

Physical properties of pepsin-solubilized types I, II, III and V collagen have been measured in acid solution at 10°C. Our results indicate that types I, II and III collagen molecules undergo a monomer-aggregate equilibrium in solution whereas type V molecules appear to attract each other but do not undergo a similar monomer-aggregate equilibrium. Interstitial collagen monomers (I, II and III) have molecular weights between $\text{280 × 10}{}^3\text{and 289 × 10}{}^3$, translational diffusion coefficients between $\text{0.820 × 10}{}^{\mathrm{?7}}\text{and 0.845 × 10}{}^{\mathrm{?7}}\text{cm}{}^2\text{s}{}^{\mathrm{?1}}$ and particle scattering factors at an angle of 175.5° and wavelength of 633 nm between 0.430 and 0.460. Type V collagen molecules after pepsin digestion were found to have a higher molecular weight ($\text{307 × 10}{}^3$), similar translational diffusion coefficient ($\text{0.860 × 10}{}^{\mathrm{?7}}\text{cm}{}^2\text{s}{}^{\mathrm{?1}}$) and similar particle scattering factor at 175.5° (0.440) to the interstitial collagens. Theoretical bead models are discussed and suggest that changes in the translational diffusion coefficient were less sensitive to bending motions than were changes in the particle scattering factor at 175.5°C. Bend angles of 50° were shown to increase the particle scattering factor by 5% whereas a bend angle of greater than 125° was required to increase the translational diffusion coefficient by 5%. Models developed from idealized shapes seen by electron microscopy of rotary shadowed collagen molecules agreed best with experimental laser light scattering measurements when the bend angles were less than 90°.