Surface properties of erythrocytes: normal, paroxysmal nocturnal hemoglobinuria and glutathione-treated cells

Affected erythrocytes of patients with paroxysmal nocturnal hemoglobinuria are deficient in the complement regulatory protein, decay accelerating factor

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired defect of bone marrow stem cells in which the affected clones produce erythrocytes (also granulocytes and platelets) with membranes that are abnormally sensitive to complement-mediated lysis. Abnormal erythrocytes (E) from patients with PNH (PNH-E) are 3-5 times more sensitive (type II PNH-E) or 15-25 times more sensitive (type III PNH-E) to lysis in vitro by human complement than normal E from unaffected individuals and the functionally normal E that arise from unaffected clones and the functionally normal E that arise from unaffected clones in PNH patients (type I PNH-E). After complement activation by either the classical or alternative pathway, abnormal amounts of C3b are deposited on the membranes of PNH-E compared with normal E, suggesting that the PNH-E membrane cannot regulate the events responsible for C3b deposition. Two proteins that decrease the stability of the classical and alternative pathway C3 convertases on target cells have been isolated from normal human E stroma: the 70,000 Mr decay accelerating factor of stroma (DAF) and the 250,000 Mr C3b receptor (C3bR). Specific immune precipitates of solubilized membranes from 125I-surface-labeled normal E demonstrate both proteins. In contrast, specific immune precipitates of PNH-E from three patients show C3bR but are deficient in DAF; type II PNH-E are relatively deficient and type III PNH-E are totally deficient in DAF. Antibody that neutralizes the activity of isolated DAF is adsorbed by intact normal E under conditions in which it is weakly adsorbed by type II PNH-E and not adsorbed by type III PNH-E. The deficiency of DAF antigen in PNH-E, as assessed by lack of immunoprecipitation and antibody adsorption, could explain the abnormal sensitivity of PNH-E to complement-mediated lysis and suggests that DAF may protect the membranes of normal E from damage resulting from autologous complement activation.

Unique profile for erythrocyte membrane acetylcholinesterase in hereditary spherocytosis

Acetylcholinesterase of human erythrocytes from healthy donors and from patients with hematological disorders was analysed in a search for differential membrane parameters. Two substrates were used to estimate the exposure of acetylcholinesterase active site in the membrane: phenylacetate, a hydrophobic substrate, to determine total enzyme activity, and acetylcholine, an ionic substrate, to measure the externally reactive enzyme. The sensitivity of acetylcholinesterase to added stearic acid was also analysed. Three categories of the disorders studied were discerned: (a) The erythrocyte acetylcholinesterase profile was indistinguishable from normal control in beta-thalassemia minor and groups of patients with autoimmune hemolytic anemia or congenital dyserythropoietic anemia type II. (b) A marked decline in acetylcholinesterase with both substrates and reduced sensitivity to stearic acid were exhibited by the erythrocytes of paroxysmal nocturnal hemoglobinuria, beta-thalassemia major and other autoimmune hemolytic anemia and congenital dyserythropoietic anemia type II patients. Normal erythrocytes, either aged or pretreated to 50 degrees C, also showed similar characteristics. (c) Hereditary spherocytosis was singly differentiated by an elevated acetylcholinesterase activity with acetylthiocholine and by a vastly diminished sensitivity to stearic acid, while activity with phenylacetate was equal to control. This distinct profile may reflect the unique organization of the erythrocyte membrane in hereditary spherocytosis.

Increased enzymatic activity of the alternative pathway convertase when bound to the erythrocytes of paroxysmal nocturnal hemoglobinuria

To investigate the greater fixation of C3 to the erythrocytes of patients with paroxysmal nocturnal hemoglobinuria (PNH) upon activation of complement, we have examined the formation and the reaction of the C3 nephritic factor-stabilized alternative pathway convertase made with purified components on normal and PNH erythrocytes. Each convertase complex converts four to five times more fluid-phase C3 to C3b when affixed to a PNH cell than when affixed to a normal cell. The greater activity of the convertase on PNH cells is not due to differences in the intrinsic or extrinsic stability of the convertase complex. The excessive binding of C3 to PNH cell si due to this increased conversion of fluid-phase C3, because the efficiency of binding of nascent C3b was identical for the two cell types. This is the first instance in which the enzyme activity of a complement complex has been shown to be increased by being affixed to an abnormal surface.

Membrane asymmetry. A survey and critical appraisal of the methodology. I. Methods for assessing the asymmetric orientation and distribution of proteins

This and the companion article are aimed at surveying the methods used for the study of membrane asymmetry. The techniques employed for the assessment of the asymmetric distribution and orientation of membrane proteins are reviewed in this article, whereas those pertaining to the unequal distribution of lipids are detailed in the companion paper. The use of immunological techniques and lectins, functions of proteins and their perturbations, chemical reagents, enzymatic isotopic labeling and enzymatic cleavage of membrane proteins and physical techniques are discussed and illustrated using recent examples of their application. Whenever appropriate, problems involving crypticity and non-availability or non-reactivity of functional sites, relevant chemical functions or protein fragments to appropriate ligands, reagents or modifying enzymes are envisaged and possible modification of the exposure of proteins during preparation of ghosts and other drawbacks are discussed, the use of different techniques and control experiments in conjunction is recommended for a more realistic assessment of the distribution and orientation of proteins.

An examination of complement proteins on membranes of paroxysmal nocturnal haemoglobinuria (PNH) and PNH-like red cells

Proteins obtained from membranes of PNH erythrocytes and of red cells treated with 2-aminoethylisothiouronium bromide (AET) following lysis in acidified serum (Ham's test) were compared by sodium dodecylsulphate-polyacrylamide gel electrophoresis. The peptide patterns were identical, providing support that AET-treated red cells afford a suitable experimental substitute for PNH red cells in studies involving complement fixation.

Ca binding to the human red cell membrane: characterization of membrane preparations and binding sites

Inside out and right side out vesicles were used to study the sidedness of Ca binding to the human red cell membrane. It was shown that these vesicles exhibited only a limited permeability to Ca, enabling the independent characterization of Ca binding to the extracellular and cytoplasmic membrane surfaces...