Conformational changes in erythrocyte membranes by prostaglandins as measured by circular dichroism

Abstract

Membranes were prepared from fresh, washed human erythrocytes by hemolysis and washing with 5 m m sodium phosphate buffer (pH 7.4). The mean residue ellipticity, [θ], of erythrocyte membrane circular dichroism was altered by prostaglandin E 1 or prostaglandin F 2α at 37 °C when observed from 250 nm to 190 nm. The decrease in negativity of [θ] with 10 −6 m prostaglandin E 1 was 12.7% at 222 nm and 17.7% at 208 nm, and with 10 −6 m prostaglandin F 2α 22.5% and 34.2%, respectively ( P < 0.01). Similar changes in [θ] were observed at lower concentrations of prostaglandins. No strict relationship between amount of change of [θ] and prostaglandin concentrations of 3 × 10 −5 m to 3 × 10 −12 m was evident. A persistent alteration of [θ] with prostaglandin was observed at 37 °C. Transient change of [θ] occurred at 25 °C with prostaglandin. No change of [θ] was observed at 15 or 20 °C. Buffer or palmitic acid were without effect on membrane [θ]. Phosphatidyl inositol or methyl arachidonate caused an increase in negativity of membrane spectra. The observed alterations of membrane [θ] did not arise from changes in light scattering as the OD 700–OD 200 of membranes was not changed by prostaglandin. Effects of prostaglandin were not dependent on light path length. The prostaglandin E 1 antagonist, 7-oxa-13-prostynoic acid, at 10 −7 m produced no change of [θ] of membrane spectra and prevented the otherwise demonstrable effects of 10 −10 m prostaglandin E 1 on [θ]. The decrease in negativity of [θ] at 222 nm is indicative of a decrease in ellipticity of membrane protein. These studies suggest that prostaglandins may act by inducing a conformational change in membrane protein.