Freeze-fracture Electron Microscopic observations on the effects of sulphydryl group reagents on human erythrocyte membranes

Abstract

The intra-membrane particles (IMPs) observed on the fracture face of frozen erythrocyte membranes are thought to correspond primarily to “band 3” tetramers or dimers. Some recent studies correlating the inhibition of water diffusion in erythrocytes by p-chloromercuribenzene sulfonate (PCMBS) with the binding of 203Hg to erythrocyte membrane proteins has enabled band 3 and the polypeptides in band 4.5 to be identified as the proteins associated with the channels for water permeation in human erythrocytes. A further characterization of the effects of the incubation of human erythrocyte membranes with PCMBS and N-ethylmaleimide (NEM) has been performed as previously described. Experimental conditions have been previously described.A comparison was made of the appearance of freeze-etched membranes of control erythrocytes and erythrocytes with the sulphydryl reagents. It was found that on many of the control and NEM-treated cells, small (50-100 nm) elevated patches could be seen (Fig. 1, 2 and 3). These are present on both fracture and etch faces and are devoid of any intramembrane particles. The patch elevations were never observed in the membranes of PCMBS-treated cells (Fig. 4).