Raman spectroscopy of intact feline corneal collagen.

The Raman Spectrum of Collagen is presented from feline corneas which were fresh and intact, heat denatured, and incubated in 2H20. Two bands in the amide I region at approx. 1630 cm-1 and approx. 1660 cm-1 and two bands at ca. 1270 cm-1 and 1247 cm-1 in the amide III region appear in the Raman spectrum of fresh and heat denatured corneal collagen. The two amide III bands have been assigned to amide III vibrations in the polar and non-polar regions of the protein. Only one small amide I band at approx. 1650 cm-1 appears when corneas are treated with 2H2O suggesting that some portion of the Raman peaks in the amide I region for corneas in water is associated with water vibrations. Feline corneal collagen fibrils do not appear to dissociate appreciably upon heating to 70 degrees C. In fact, heated corneas appear structurally similar to corneas aged 30 h at 50 degrees C. We suggest that the swelling induced by heating and aging is predominantly caused by water being absorbed and remaining between the collagen fibrils, causing a slightly more disordered collagen matrix.