Characteristics of BCθ binding to intact cells. (a)
BCθ binding depends on cholesterol contents in cell membranes.
Cholesterol was depleted from platelets with 5, 10, and 20 mM
2OHpβCD. The amount of BCθ bound to the platelets was quantified by
flow-cytometric analysis (Inset) using
fluorescein–avidin and plotted against cholesterol content. The values
are expressed as percentage of nontreated control. Cholesterol in
untreated platelets was 33 mol% of total lipids. (b)
BCθ bound to cells was retained in the Tx-insoluble fraction. After
incubation with BCθ, platelets, erythrocytes, MOLT-4, and A431 cells
were extracted with 1% Tx (4°C or 37°C) or 60 mM octyl glucoside
(OGD) (4°C) and the insoluble fraction was separated by
centrifugation at 15,000 × g. The distribution of
BCθ in insoluble pellet and soluble fractions were determined. T,
total; P, pellet; S, soluble fractions.