Effect of transmembrane ion gradients on Raman spectra of sealed, hemoglobin-free erythrocyte membrane vesicles.

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Abstract
Sealed Hb-free [human] erythrocyte vesicles were isolated. Imposition of transmembrane cation gradients increased the intensity of Raman scattering in the CH3-stretching region as observed with unsealed ghosts at temperatures > 38.degree. C and pH < 7.0. Modifications in the amide I and amide III frequencies consistent with increased helicity of membrane proteins were observed upon imposition of a cation gradient. Spectrin-free vesicles also demonstrated cation gradient-sensitive intensity changes in the CH3-stretching region. No evidence for cation gradient-related protein conformation changes was found with these vasicles. The transmembrane potential of these vesicles was altered by variations in anion composition and the electrogenic activity of Na+,K+-ATPase. The membrane potential was monitored by cyanine dye fluorescence. Imposition of a membrane potential (negative inside) also increased the intensity of Raman scattering in the CH3-stretching region. A transmembrane potential (negative inside) and/or cation gradient can apparently energize membranes by compression of the apolar region and transfer of protein methyl residues into polar regions.

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