Effect of alkaline pH on the optical properties of native and modified erythrocyte membranes.

In circular dichroism (CD) spectra of erythrocyte membranes, the intensity of the 208-nm transition was found to increase with pH, in the region above 9.5. This effect, which in native membranes is only partially reversible, was not observed if the membranes had previously been exposed to 70' at neutral pH, or treated with formaldehyde; in both these cases, the intensity of the whole CD spectrum was decreased. Using chloroform-methanol-treated membranes, which from their infrared (ir) characteristics appeared to be partially in a p conformation, it was possible to correlate the alkali-induced variations of the CD spectrum to modifications of the ir spectrum. The results are discussed in terms of a depolymerization of the membranes at high pH, or of a pH-dependent transition of membrane proteins toward a larger amount of random coil conformation.