Evidence against a generalized membrane defect in dystrophic mice platelets

Arrhenius plots of acetylcholinesterase activity in mammalian erythrocytes and in Torpedo electric organ. Effect of solubilization by proteinases and by a phosphatidylinositol-specific phospholipase C

The temperature-dependence of the catalytic activity of acetylcholinesterase (AChE) from rat erythrocyte-ghost membranes and from Torpedo electric-organ membranes was examined. In the case of rat erythrocyte AChE, a non-linear Arrhenius plot was observed both before and after solubilization by a phosphatidylinositol-specific phospholipase C or by proteinase treatment. Similarly, no significant differences were observed in Arrhenius plots of Torpedo electric-organ AChE before or after solubilization. These results support our suggestion that the catalytic subunit of AChE does not penetrate deeply into the lipid bilayer of the plasma membrane and also suggest that care must be taken in ascribing break points in Arrhenius plots of membrane-bound enzymes to changes in their lipid environment.

A study of platelet protein phosphorylation in Duchenne muscular dystrophy. Further evidence against the generalised membrane defect theory

As a test of the generalised defect theory for Duchenne muscular dystrophy (DMD), basal and calcium-dependent platelet protein phosphorylation was examined in order to determine if the increased concentration of calcium in DMD skeletal muscle is reflected in DMD platelets. Protein phosphorylation was quantitated by gradient slab gel electrophoresis and autoradiography. The number of phosphoproteins in each phosphoprotein peak was determined by comparison with two-dimensional gel electrophoresis. Many phosphoprotein peaks were present in unstimulated platelet preparations both in whole platelet homogenates and in intact platelets. Two of these phosphoprotein peaks were calcium-dependent, one was a single phosphoprotein, the other consisted of 4 phosphoproteins. No disease-related differences were observed in either basal or calcium-stimulated phosphoproteins. These results do not support previous reports of platelet abnormalities in DMD, and provide further evidence that the biochemical defect in Duchenne muscular dystrophy is neither generalised nor a membrane defect. The biochemical defect in DMD should be regarded as a skeletal muscle abnormality until proved otherwise.

Concanavalin A binding sites on the erythrocytes of normal and genetically dystrophic chickens

Red blood cells (RBCs) were obtained from genetically dystrophic chickens (Dy) and age-matched controls (C). Dy-RBCs had a lower titer of agglutination to concanavalin A (Con A) compared to C-RBCs. In order to ascertain the difference in agglutination, Con A binding on RBCs was studied, using 125I-labeled Con A ([125I]Con A) and ferritin conjugate to Con A (Fer-Con A). Kinetic analysis of [125I]Con A binding to Dy-RBCs showed a reduction of major binding sites of Con A. There was no difference in the apparent association constant for the major binding sites of Con A between Dy-RBCs and C-RBCs. Quantitative analysis of Con A binding site distribution on RBCs using Fer-Con A showed a remarkable diminution of ferritin particles tagged on the surface of Dy-RBCs. There was no significant difference in the distribution pattern of ferritin particles between Dy-RBCs and C-RBCs.