Studies of serum and erythrocyte membrane proteins in cystic fibrosis and Duchenne muscular dystrophy

Abstract

(I) Recent research on Duchenne muscular dystrophy lends support to the notion that the genetic defect may affect the surface membranes of not only muscle cells but other cells particularly erythrocytes. Abnormalities in the content and compositions of fatty acids and phosphorylations of some erythrocyte membrane laroteins have been reported in support of this hypothesis. SDS gel electrophoresis patterns of erythrocyte membrane proteins from Duchenne muscular dystrophy were reported to be normal. In this report, SDS gel electrophoresis of erythrocyte membrane proteins prepared by hypotononic lysis of red blood cells at pH8, were not able to show any differences between samples from Duchenne muscular dystrophy patients and those from normal control subjects. The relative intensities of the protein bands varied from preparation to preparation but did not follow a pattern that could distinguish control samples from test samples. Two dimensional gel electrophoresis of completely denatured erythrocyte membrane proteins resolved over 150 peptides in 9% gels and over 200 peptides in gels above 12%, but no consistent differences were observed between Duchenne muscular dystrophy samples and those from control subjects. (II) Although cystic fibrosis is the most frequent lethal genetic syndrome among caucasian children, there is no known biochemical or structural defect to account for all its pathophysiological phenomena. Previous reports in other laboratories have shown that a cystic fibrosis protein (CFP) could be demonstrated in sera of over 90% of cystic fibrosis homozygotes by isoelectric focusing. The protein was characterised as having a molecular weight of between 3000-10 000 and pi near pH8.4. Our isoelectric focusing results demonstrated the protein, pI8.5, in 40% of the homozygotes, thus supporting the view that the procedure is not a useful diagnostic tool and that the "cystic fibrosis protein" is not a specific marker for the disorder. We extended this investigation by labellings, with 125I, all the serum Proteins that focused between pH8 and pH9 and then running the labelled proteins in some 15% SDS gels. The results we obtained could not distinguish cystic fibrosis samples from normal control ones. Some studies have suggested that a mutant form of alpha-2-macroglobulin could be the primary defect in cystic fibrosis and also in multiple sclerosis. To test for the presence of charge or size mutations, alpha-2-macroglobulin was subjected to extensive investigations by (i) SDS gel electropihoresis of its heat fragments, (ii) two dimensional gel electrophoresis following complete denaturation and (iii) immune- electrofocusing of its native form. Alpha-2-macroglobulin from cystic fibrosis patients could not be distinguished from that obtained from normal control subjects but that from multiple sclerosis patients showed some different patterns. The significance of the abnormality of ?2M from multiple sclerosis patients needs further investigations. Extensive two dimensional gel electrophoresis of whole serum following complete denaturation were performed but the results did not reveal any consistent differences between cystic fibrosis and multiple sclerosis patients and normal control subjects.