A sharp cell surface conformational transition at low ionic strength changes the nature of the adhesion of enzyme-treated red blood cells to a hydrocarbon interface.

Aldehyde-fixed human red cells have previously been used to assess the roles of electrostatic and electrodynamic forces in adhesion. We have attempted to test the prediction that enzymic removal of cell surface negative charges should increase adhesion in dilute salt solutions by reducing electrostatic repulsion. While this is indeed the case for neuraminidase-treated cells and also for Pronase- and trypsin-treated cells over much of the low ionic strength range, the latter two treatments cause very strong adhesion over a remarkably narrow range of ionic strength centred on 1 mM-NaCl. At 0.5 and 1.5 mM adhesion is negligible. After Pronase treatment a further adhesive peak occurs at 2.5 mM. Electrophoresis of protease-treated cells shows small but clear reductions in mobility at precisely these peak adhesion values. These electrophoretic potential changes are almost certainly not large enough to cause increased adhesion directly, and it is thought that they are second-order changes, symptomatic of a structural rearrangement of the cell surface. How this causes such vastly augmented adhesion is an intriguing problem.