JBC, Vol. 250, Issue 16, 6256-6263, Aug, 1975
Arrangement of human erythrocyte membrane proteins
E. Reichstein and R. Blostein
The orientation of human erythrocyte membrane protein was examined by
enzymic iodination using lactoperoxidase with the glucose-oxidase system
for generating peroxide, followed by proteolytic digestion. The outer
surface of intact cells was labeled with 125I and the cytoplasmic surface
of either resealed ghosts containing lactoperoxidase or of inside-out
vesicles was labeled with 131I. Following iodination, the outer surface
(resealed ghosts) or the cytoplasmic surface (outer surface of inside-out
vesicles) was digested with trypsin, chymotrypsin, or pronase. Sodium
dodecyl sulfate gel electrophoresis of the isolated membranes revealed
three major and several minor peaks of radioactivity. Their surface
orientation, defined within the limits of the specificity of the probes
used, was as follows: the three major peaks consist of: (a) a 90,000 to
100,000 molecular weight component labeled on both surfaces; its
proteolytic digestion profile indicated that it spans the membrane in an
asymmetric manner and that it is composed of more than one peptide; (b) the
major red cell membrane glycoprotein (apparent molecular weight 60,000)
which is labeled and digested at only the outer surface; and (c) peptide(s)
of high molecular weight (approximately 200,000), labeled and digested at
only the cytoplasmic surface. The minor components include a glycoprotein
of approximately 25,000 (apparent molecular weight) accessible to both
surfaces and peptides of 60,000 to 70,000, 45,000, and 20,000 molecular
weight labeled only on the inner surface.