Thermodynamic behaviour of membrane enzymes in Duchenne muscular dystrophy

Immunoglobulins from patients with amyotrophic lateral sclerosis affect human erythrocyte acetylcholinesterase

Human erythrocyte acetylcholinesterase (AChE) solubilized with Triton X-100 and obtained as a complex with micelles containing Triton and membrane phospholipids was incubated with immunoglobulins (Igs) from patients with amyotrophic lateral sclerosis (ALS) and from normal individuals. The temperature dependence of the AChE activity was determined. Biphasic (broken) Arrhenius plots were obtained with control Igs with the break point at 32.8 +/- 0.3 degrees C (SD, n = 18) indicating that the enzyme changes its conformation at this temperature. With ALS-Igs monophasic (linear) plots were observed in 14 cases and a biphasic in one case. ALS-Igs prevent the conformational change occurring at the break point temperature. The activation energy at physiological temperature increased by 60% from 2.4 to 3.8 kcal/mol (10.0-15.9 kJ/mol) which implies that ALS-Igs inhibit AChE. Thus, ALS-patients have autoantibodies that change the normal behaviour of erythrocyte AChE and which bind to the enzyme molecule or/and to phospholipids associated with the enzyme. At least part of the autoantibodies should be directed against the enzyme molecule, since a change in the Arrhenius plot was also observed in a control experiment with AChE which probably had micelles without any phospholipids. This enzyme was isolated by affinity chromatography and was washed with a buffer containing Triton X-100 before desorption from the affinity column, a treatment known to remove all phospholipids from erythrocyte AChE.

5'-Nucleotidase in skin fibroblasts from patients with Duchenne muscular dystrophy

The 5'-nucleotidase of plasma membranes of cultured skin fibroblasts from patients with Duchenne muscular dystrophy had a reduced affinity for its substrate, 5'-AMP. The Arrhenius plot of the temperature dependence of this enzyme activity was normal. There was no difference between patients and controls in the specific 5'-nucleotidase activity in the whole cell homogenates.

Superoxide dismutases, glutathione peroxidase, and catalase in neuromuscular disease

Studies in experimental muscular dystrophy indicate a possible role for anomalous redox metabolism in the genesis of these disorders, prompting a retrospective review of changes in redox-active enzymes in Duchenne muscular dystrophy (DMD). Both manganous and copper-zinc superoxide dismutase (Mn and CuZn SOD) content and glutathione peroxidase and catalase activities were measured in muscle biopsy specimens taken from normal individuals and from patients with Duchenne muscular dystrophy and other neuromuscular diseases. Muscle from patients with Duchenne dystrophy differed from the norm in that both Mn SOD and CuZn SOD were decreased and glutathione peroxidase was increased. This profile differed from that in anterior horn cell diseases in that CuZn SOD was not decreased in these disorders and from polymyositis, where CuZn SOD was decreased without an increase in glutathione peroxidase. Thus, there appears to be disease-specific changes in these enzymes in DMD. These data support the concept that changes in redox-active enzymes may be associated with the genesis of DMD.

Some biophysical properties of the erythrocyte membrane in Duchenne muscular dystrophy

Inasmuch as prior authors have suggested a 'generalized membrane defect' in patients with Duchenne muscular dystrophy, this study was undertaken to examine some biophysical properties of the erythrocytes in affected individuals. Using the micropipette technique we investigated the rheological properties of erythrocytes from 11 Duchenne muscular dystrophy patients (boys 3-14 years old) and 5 carriers (mothers 20-42 years old). The mean elastic modulus and membrane viscosity of the patient's erythrocytes were not significantly different from those of a group of 8 unaffected age-matched boys. The carrier group did not differ significantly from the adult control group in any of the rheological parameters. A significant increase in the number of stomatocytes was observed in the patient group, and a similar trend (not statistically significant) was observed in the carrier group. The membrane lipid fluidity of erythrocytes from patients, carriers, and normal controls was assessed with three different probes by fluorescence depolarization, and no significant differences were found. Our results indicate that there is a progressive elevation of the membrane elastic modulus with increasing age of the patients: the younger patients have a lower elastic modulus than their age-matched controls, while the older patients have a higher elastic modulus than their age-matched controls.

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 spin label study of the erythrocyte membrane in mothers and sisters of patients suffering from Duchenne Muscular Dystrophy

The erythrocyte membranes of mothers and sisters of boys suffering from Duchenne Muscular Dystrophy (DMD) have been studied by spin labelling. Two oxazolidine nitroxide derivatives of stearic acid were used. With the first of them (16 NS) which probes the hydrophobic part of the phospholipids, we measured the fluidity of the membrane as a function of temperature. The second nitroxide derivative (5 NS) probes the membrane near the phospholipid polar heads. The amplitude of the electron spin resonance signal was studied as a function of the spectrometer microwave power in order to determine the paramagnetic label saturation behaviour. No significant difference was observed between the control adult women and the carrier mothers. On the contrary, almost all the normal young premenarchial girls showed simultaneously a break in the fluidity vs. temperature plot of the 16 NS probe and a saturation phenomenon of the 5 NS label signal. In about 50% of the DMD boys' sisters, no break in the temperature plot nor saturation behaviour was observed. This corresponds to the theoretical repartition between normal and carrier girls if one admits that about 30% of the latter do not have any detectable membrane abnormality, as in the case of the creatine kinase (CK) test which shows about 30% of normal levels in carrier women. The study of the erythrocyte membrane in young girls can then be an useful complementary tool to detect DMD carriers.

Duchenne muscular dystrophy: pathogenetic aspects and genetic prevention

Duchenne muscular dystrophy (DMD) is the most common sex linked lethal disease in man (one case in about 4000 male live births). The patients are wheelchair bound around the age of 8-10 years and usually die before the age of 20 years. The mutation rate, estimated by different methods and from different population studies, is in the order of 7 X 10(-5), which is higher than for any other X-linked genetic disease. Moreover, unlike other X linked diseases such as hemophilia A or Lesh-Nyhan's disease, there seems to be no sex difference for the mutation rates in DMD. Several observations of DMD in girls bearing X-autosomal translocations and linkage studies on two X chromosomal DNA restriction fragment length polymorphisms indicate that the DMD locus is situated on the short arm of the X chromosome, between Xp11 and Xp22. It may be of considerable length, and perhaps consisting of actively coding and non-active intervening DNA sequences. Thus unequal crossing over during meiosis in females could theoretically account for a considerable proportion of new mutations. However, there is no structurally or functionally abnormal protein known that might represent the primary gene product, nor has any pathogenetic mechanism leading to the observed biochemical and histological alterations been elucidated. Among the numerous pathogenetic concepts the hypothesis of a structural or/and functional defect of the muscular plasma membrane is still the most attractive. It would explain both the excess of muscular constituents found in serum of patients and carriers, such as creatine kinase (CK), as well as the excessive calcium uptake by dystrophic muscle fibres, which, prior to necrosis, could lead to hypercontraction, rupture of myofilaments in adjacent sarcomeres and by excessive Ca uptake to mitochondrial damage causing crucial energy loss. The results of studies on structural and functional membrane abnormalities in cells other than muscle tissue, e.g., erythrocytes, lymphocytes and cultured fibroblasts, indicate that the DMD mutation is probably demonstrable in these tissues. However, most of the findings are still difficult to reproduce or even controversial. DMD is an incurable disease; therefore most effort, in research as well as in practical medicine, is concentrated upon its prevention.(ABSTRACT TRUNCATED AT 400 WORDS)