ELECTRIC PROPERTIES OF PHOTOAFFINITY-LABELED PANCREATIC A-SUBTYPE CHOLECYSTOKININ

Although the isoelectric point of a protein is very important, electric focusing of intrinsic membrane proteins in polyacrylamide or agarose gels often fails. The recently introduced Bio-Rad Rotofor cell allowed isoelectric focusig of such a protein, cholecystokinin (CCK) receptor. Both the isoelectric point and the molecular weight (Mr) of pacreatic CCK receptor were determined. For this purpose, membrane CCK receptor was photoaffinity labelled by a cleavable agonist probe, subsequently prepurified on immobilized wheat germ agglutinin and analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis and isoelectrofocusig in solution in the presence of Nonidet P-40. CCK receptor was identified at Mr 85 000-100 000, whereas its deglycosylated product was shifted to M4 42 000. Further, the isoelectric poits of the glycosylated and deglycosylated forms of CCK receptor were pH 4.8 and 4.3, respectively. A knowledge of the isolelectric point should help in characterizing better CCK receptor heterogeneity and/or in purifying CCK receptor proteins. © 1990.