ERYTHROCYTE-MEMBRANES UNDERGO COOPERATIVE, PH-SENSITIVE STATE TRANSITIONS IN PHYSIOLOGICAL TEMPERATURE-RANGE - EVIDENCE FROM RAMAN-SPECTROSCOPY

The Raman scattering from erythrocyte ghosts was measured at 2700-3000 cm-1 (CH-stretching region). Plots of the intensity (I) of the 2930 cm-1 band relative to the intensity of the thermally stable 2850 cm-1 band, i.e., the [I2930/I2850] ratio, as a function of temperature reveal a sharp discontinuity, which at pH 7.4 has a lower limit of 38.degree. and is irreversible above 42.degree.. [I2930/I2850] is stable between pH 7.0 and pH 7.4, but increases or decreases sharply below pH 7.0 or above pH 7.5, respectively. Reduction of pH to 6.5 lowers the transition temperature by about 16.degree., and a shift to pH 6.0 drops the transition range to 0-7.degree.. The above effects of temperature and pH on Raman scattering closely correspond to those detected by studies on the interaction of membrane protein fluorophores and lipid-soluble fluorescence quenchers. Taken together, these results suggest that the transitions represent concerted processes, involving hydrophobic amino acid residues and lipid chains at apolar protein-lipid boundaries.