The effects of pH and temperature on the circular dichroism of human erythrocyte membranes.

The effects of pH and temperature on the structure of human erythrocyte membranes were studied by circular dichroism (CD). The results obtained demonstrate that the membrane CD spectra undergo significant changes when the pH of the solution deviates from its native pH range of 7 to 8. Spectral changes in the acidic pH region include drastic reductions and slight shifts in the CD signal which may reflect a decrease in alpha-helical content of the proteins and/or an increase in optical artifacts, both of which are irreversible. In the alkaline pH region, dramatic increases in ellipticity and blue-shifts in the spectra are observed between pH 8 and 10. In addition, the spectra more closely resemble those reported for membrane samples where the spectral distortions have been removed. The changes in the alkaline region are demonstrated to be only partially reversible and may be due to conformational alterations in the membrane proteins and/or to a reduction in optical distortions. Thermal stability studies reinforce the irreversible behavior of the membrane samples.