Theoretical π‐π* absorption, circular dichroic, and linear dichroic spectra of collagen triple helices

Absorption, CD, and LD spectra of the π‐π* transition near 200 nm are calculated for poly(Gly‐X‐Y) (X,Y = Gly, Ala, Pro) in four conformations proposed for collagen like triple helices in the recent literature. A dipole interaction model is used with the same optical paramenters as in previous studies of polypeptide spectra. The CD spectra are sensitive to backbone structure and amino acid composition, although the experimentally observed negative peak near 200 nm is a general feature of most the calculated spectra. Interchain interactions significantly affect the CD spectra in most cases. Calculations for (Gly‐Pro‐Ala)3 and (Gly‐Ala‐Pro)3 in the triple helical structure of Fraser, MacRae, and Suzuki [(1979) J. Mol. Biol. 129, 463–481] show absorption, CD, and LD spectra in fairly good agreement with experiment. The characteristics of the π‐π* normal modes responsible for the calculated spectra are compared with those of the component bands resolved from the experimental spectra of collagen by Mandel and Holzwarth [(1973) Biopolymers 12, 655–674].