Escherichia coli cu-hemolysin (HlyA) can lyse both red blood cells (RBC) an
d liposomes, However, the cells are lysed at HlyA concentrations 1-2 orders
of magnitude lower than liposomes (large unilamellar vesicles). Treatment
of RBC with trypsin, but not with chymotrypsin, reduces the sensitivity of
RBC toward HlyA to the level of the liposomes, Since glycophorin, one of th
e main proteins in the RBC surface, can be hydrolyzed by trypsin much more
readily than by chymotrypsin, the possibility was tested of a specific bind
ing of HlyA to glycophorin, With this purpose, a number of experiments were
performed. (a) HlyA was preincubated with purified glycophorin, after whic
h it was found to be inactive against both RBC and liposomes, (b) Treatment
of RBC with an anti-glycophorin antibody protected the cells against HlyA
lysis, (c) Immobilized HlyA was able to bind glycophorin present in a deter
gent lysate of RBC ghosts. (d) Incorporation of glycophorin into pure phosp
hatidylcholine liposomes increased notoriously the sensitivity of the vesic
les toward HlyA (e) Treatment of the glycophorin-containing liposomes with
trypsin reverted the vesicles to their original low sensitivity, The above
results are interpreted in terms of glycophorin acting as a receptor for Hl
yA in RBC. The binding constant of HlyA for glycophorin was estimated, in R
BC at sublytic HlyA concentrations, to be 1.5 x 10(-9) M.