Abstract
The formation and stabilization of a complex between total erythrocyte apoprotein and monolayers of total erythrocyte lipid as measured by changes of surface pressure (ΞΟ) and rate of change of surface pressure (dΟ/dt) was studied as a function of pH, ionic strength, and lipid surface pressure. Penetration of apoprotein into lipid monolayers was favored by conditions in which lipid and apoprotein were oppositely charged. Once the interaction was completed, the resultant surface complex was resistant to large changes in subphase pH and ionic strength as shown by the insensitivity of ΞΟ to these parameters. The dΟ/dt, however, showed strong dependence on pH and ionic strength, but not on lipid surface pressure. A sharp decrease in dΟ/dt around pH 3.5β4.5 is associated with the change in apoprotein charge from (+) to (β). Comparison of complex formation between apoprotein and bovine serum albumin, cytochrome c, and human hemoglobin suggests that erythrocyte apoprotein was specialized in its interaction with erythrocyte lipids. The data show that formation of an apoproteinβlipid complex at the airβwater interface has both electrostatic and hydrophobic components. This contradicts results from other laboratories studying erythrocyte membrane recombination by bulk methods.