The dissociation of peripheral proteins from erythrocyte membranes brought about by p-mercuribenzenesulfonate

Hemolysis of human erythrocytes with saponin affects the membrane structure

Incubation of cells and tissues with saponin makes the lipid bilayer permeable to macromolecules. Ghosts (membrane preparations) of saponin-lysed erythrocytes do not reseal, thus indicating an irreversible damage of the lipid bilayer. We investigated the influence of disturbance of the lipid bilayer on membrane proteins by comparing ghosts of saponin-lysed erythrocytes with ghosts of cells lysed in hypotonic buffer. Transmission electron microscopy revealed destruction of the lipid bilayer and emergence of multilamellar buds in saponin-lysed ghosts. Freeze-fracture electron microscopy showed regions with crystalline lipids and an increase in particle-free areas on fracture faces. The number of protein sulfhydryl groups and the binding of hemoglobin were diminished in saponin-lysed ghosts. A Scatchard plot of hemoglobin binding revealed the decrease of high affinity binding sites. All these results indicate an aggregation of band 3 protein also demonstrated by laser scanning microscopy after incubation of cells labelled with eosin-5-maleimide with sublytic concentration of saponin. Hemolysis with saponin also affected the interaction between transmembrane proteins and the cytoskeleton. Dissociation of peripheral membrane proteins by incubation of ghosts in low salt buffer or by blocking sulfhydryl groups was increased and the association of spectrin with spectrin-depleted vesicles was decreased. The increased incorporation of the fluorescent probe Merocyanine 540 into saponin-lysed ghosts and the increased relative fluorescence quantum yield confirmed the perturbation of the lipid bilayer and the changed interaction between membrane lipids and intrinsic membrane proteins. Our results suggest that permeabilization of the lipid bilayer with saponin to admit the access of antibodies to the cytoplasmic surface of cells can aggregate transmembrane proteins and affect the immunocytochemical localization of associated proteins of the cytoskeleton.

Red cell membrane protein band 4.2: phenotypic, genetic and electron microscopic aspects

The present status of band 4.2 has been reviewed from the standpoint of protein chemistry, gene analysis and clinical hematology. Band 4.2 plays an important role in various cellular functions. In 142 GCT-->ACT band 4.2 deficiency, abnormalities of the cytoskeletal network were clearly observed by electron microscopy and by ektacytometry, although the cytoskeletal proteins themselves were essentially normal in these red cells. The physiological states of band 3 in situ in the membranes were also affected in band 4.2 deficiency, as detected by electron microscopy, although again the biochemical properties of band 3 itself were essentially normal in these red cells. Other disorders of band 4.2 deficiency in the absence of the 142 GCT-->ACT mutation appear to be most interesting in the pathogenesis of hemolysis. In some of the band 4.2 anomalies, other membrane proteins including band 3 would appear to be most pathognomonic for the disease states. These conditions require elucidation by protein chemistry and gene analysis. The control mechanism of the gene expression should also be clarified to understand the important role of band 4.2 in health and disease.

pH-induced denaturation of spectrin changes the interaction of membrane proteins in erythrocyte ghosts. Biochemical and electron microscopic evidence

The influence of different buffer pH values on the properties of spectrin in erythrocyte ghosts and on isolated spectrin was investigated. Ultrastructural findings and the results of biochemical studies show that denaturation and aggregation of spectrin molecules rather than disulfide crosslinking are responsible for the precipitation of spectrin in acidic buffer. Since hemolysis in hypotonic buffer at pH 6.0 yields ghosts with spicules and microvesicles, the structure of spectrin in intact cells might also be changed and lead to the clustering of transmembrane proteins and the aggregation of components of the cytoplasmic network.

Involvement of cytoskeletal proteins in the barrier function of the human erythrocyte membrane. II. Formation of membrane leaks in ghost membranes after limited proteolysis of skeletal proteins by trypsin

Limited proteolysis of human erythrocyte ghost membranes by low levels of trypsin (10-240 ng/ml) added bilaterally at 0 degrees C together with the proteinase inhibitor, phenylmethylsulfonyl fluoride (PMSF) before resealing at 37 degrees C leads to a graded digestion of spectrin and ankyrin and the disappearance of band 4.1 protein, while band 3 is cleaved only to a very low extent. These alterations are accompanied by an increase of membrane permeability of the resealed ghosts to hydrophilic nonelectrolytes (erythritol to sucrose), taken to reflect impaired resealing. Moreover, the membrane begins to vesiculate. Shedding of vesicles during the efflux measurements can not be responsible for the increased release of test solutes, since the ghosts do not loose hemoglobin and discriminate the nonelectrolytes according to their size. Moreover, the vesiculation site itself does not seem to act as the leak site, since ghosts prepared from erythrocytes pretreated with a carbodiimide which induces membrane rigidification still exhibit a pronounced protein degradation and vesiculation while the permeability enhancement induced by trypsination is markedly suppressed. The trypsin-induced leak has the properties of an aqueous pore as indicated, besides size selectivity, by its inhibition by phloretin and the very low activation energy. In analogy with concepts developed in the preceding paper (Klonk, S. and Deuticke, B. (1992) Biochim. Biophys. Acta 1106, 126-136 (Part I in this series)) the impaired resealing after limited proteolysis is assumed to be related to a perturbation of interactions of membrane skeletal elements with themselves and/or with the bilayer domain constituting the permeability barrier.

Effect of pCMBS on anion transport in human red cell membranes

The kinetics of binding of the mercurial sulfhydryl reagent, pCMBS (p-chloromercuribenzene sulfonate), to the extracellular site(s) at which pCMBS inhibits water and urea transport across the human red cell membrane, have previously been characterized. To determine whether pCMBS binding alters Cl- transport, we measured Cl-/NO3- exchange by fluorescence enhancement, using the dye SPQ (6-methoxy-N-(3-sulfopropyl)quinolinium). An essentially instantaneous extracellular phase of pCMBS inhibition is followed by a much slower intracellular phase, correlated with pCMBS permeation. We attribute the instantaneous phase to competitive inhibition of Cl- binding to band 3 by the pCMBS anion. The ID50 of 2.0 +/- 0.1 mM agrees with other organic sulfonates, but is very much greater than that of pCMBS inhibition of urea and water transport, showing that pCMBS reaction with water and urea transport inhibition sites has no effect on anion exchange. The intracellular inhibition by 1 mM pCMBS (1 h) is apparently non-competitive with Ki = 5.5 +/- 6.3 mM, presumably an allosteric effect of pCMBS binding to an intracellular band 3-related sulfhydryl group. After N-ethylmaleimide (NEM) treatment to block these band 3 sulfhydryl groups, there is apparent non-competitive inhibition with Ki = 2.1 +/- 1.2 mM, which suggests that pCMBS reacts with one of the NEM-insensitive sulfhydryl groups on a protein that links band 3 to the cytoskeleton, perhaps ankyrin or bands 4.1 and 4.2.

Solubilization and denaturation of monomeric actin from erythrocyte membranes by p-mercuribenzenesulfonate

Solutions of p-mercuribenzenesulfonate extract the peripheral proteins from the red cell membrane in a water-soluble form. Low concentrations of the reagent selectively solubilize actin, while at higher concentrations, spectrin, ankyrin and bands 4.2 and 4.1 are extracted. After brief exposure to the reagent, followed by displacement of the mercurial with dithiothreitol or 2-mercaptoethanol, the soluble actin is capable of inhibiting DNAse I activity. With prolonged exposure or with higher concentrations of the reagent, the ability to inhibit DNAse is gradually lost. The kinetics of both the release of actin capable of DNAse inhibition and the subsequent loss of that capability are pseudo-first-order with respect to time, but show second-order dependence on the concentration of mercurial. These data suggest that dissociation of the actin from protofilaments in the cytoskeleton requires exposure of more than one sulfhydryl group to the reagent. Subsequent inactivation also appears to be dependent on the reaction of further multiple sulfhydryl groups, possibly in buried regions of the actin molecule.