EFFECTS OF DIMETHYL-SULFOXIDE, GLYCEROL, AND ETHYLENE-GLYCOL ON SECONDARY STRUCTURES OF CYTOCHROME-C AND LYSOZYME AS OBSERVED BY INFRARED-SPECTROSCOPY

Effects of 10-30% (v/v) of dimethyl sulfoxide, glycerol, and ethylene glycol on the H-O-H bending vibration of water and the amide I bands o f horse heart cytochrome c and chicken egg white lysozyme in 25 mM sod ium phosphate buffer (pH 7.4) were examined at 20 degrees C by Fourier transform infrared spectroscopy. The H-O-H bending mode of water was strongly affected by these cryoprotectant solvents. Increasing the con centration of cryosolvents from 0 to 30% shifts the water bending band maximum from 1645 to about 1650 cm(-1). Second-derivative analysis re veals significant changes in conformation-sensitive amide I regions of lysozyme ascribed to ex-helix (1657 cm(-1)), turn (1674 cm(-1)), and unordered (1646 cm(-1)) structures; each cryosolvent increases the int ensity of the 1657 cm(-1) band at the expense of bands at 1674 and 164 6 cm(-1). No changes in spectra deemed significant were observed for c ytochrome c under the same conditions. There is no spectral evidence o f structural randomization of proteins due to the presence of these cr yosolvents. Cryosolvent-induced changes in secondary structure of prot eins may result from changes in water structure which, in turn, pertur b the structure of the protein and/or from direct interactions between cryosolvent and protein.