The behaviour of glycophorin at the air—water interface

Abstract

The properties of the major erythrocyte sialoglycoprotein glycophorin, at the aqueous—air interface have been investigated. Using radiolabelled 14C-glycophorin the rate of adsorption has been shown to be largely diffusion controlled and to depend on the ionic composition of the aqueous substrate. The surface concentration increases in the substrate sequence 0.1 M NaCl < 1 M NaCl < 1.6 M ammonium sulphate. The extent of adsorption to the aqueous—air interface is pH dependent and increases on either side of pH 4, whereas spread films of glycophorin have a minimum area per molecule at pH 4.5. Spreading experiments show that glycophorin desorbs from the interface at high surface concentrations (>2 mg m−2). Surface pressure—area isotherms are anomalous in exhibiting reproducible and reversible non-quantitative spreading behaviour. The isotherms become move compressed with increasing initial surface concentration. These observations are discussed in terms of the aggregation ofglycophorin molecules at the interface. When spread on 1.6 or 3.2 M ammonium sulphate at low initial surface concentration (∼0.05 mg m−2) the isotherms are consistent with the view that the glycophorin molecule is anchored at the interface by more than the hydrophobic 22 amino acid residue trans-bilayer domain.