Interaction of p-aminobenzoic acid with erythrocyte membrane: photoaffinity labeling of the binding sites.
p-Aminobenzoic acid (PABA) was found to prevent eichinocytosis of red cells in vitro. Equilibrium binding studies with right-side-out membrane vesicles revealed a similar number of binding sites and Kd values for both normal and sickle cell membranes. A [14C]Azide analog of PABA was synthesized as a photoaffinity label to probe its sites of interaction on the erythrocyte membranes. Competitive binding studies of PABA with its azide indicated that both the compounds share common binding sites on the membrane surface. The azide was found to covalently incorporate into the membrane components upon irradiation; 52-35% of the label was associated with the proteins and the remaining with the lipids. Electrophoretic analysis of photolabeled membranes revealed that the azide interacts mainly with Band 3 protein in the case of intact erythrocytes and right-side-out sealed vesicles; however, if unsealed ghosts are used, other membrane proteins besides Band 3 are photolabeled. PABA was found to inhibit both high and low affinity calcium-binding sites situated on either surface of the membrane apparently in a non-competitive manner. However, calcium binding stimulated by magnesium and ATP was only slightly affected. Calcium transport into inside-out vesicles was inhibited by PABA, but it did not affect the calcium ATPase activity.
Premachandra
B R
BR
Department of Biochemistry, University of the Pacific, San Francisco, California 94115.
D010129:4-Aminobenzoic Acid / Q000494:pharmacology*; D000345:Affinity Labels; D062365:Aminobenzoates / Q000494:pharmacology*; D001665:Binding Sites; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004910:Erythrocyte Membrane / Q000187:drug effects* / Q000378:metabolism; D004913:Erythrocytes, Abnormal / Q000187:drug effects; D006801:Humans; D010782:Photolysis
D000345:Affinity Labels; D062365:Aminobenzoates; D002118:Calcium; D010129:4-Aminobenzoic Acid