Monosaccharide transporter of the human erythrocyte. Characterization of an improved preparation

Abstract

The human erythrocyte monosaccharide transporter has been purified through the use of the dialyzable detergent octyl glucoside. It was found that the transporter denatures in the detergent and that the rate of this process could be reduced by increasing the ratio of phospholipid to detergent. The transporter was obtained in higher yield and with a higher specific activity for cytochalasin B binding than has been previously reported. Scatchard plot analysis of cytochalasin B binding to the reconstituted preparations gave a dissociation constant of 1.5 X 10(-7) M, and there were found to be 15.3 nmol of sites/mg of protein. On the basis of a value of 46 000 for the molecular weight of the polypeptide, this specific activity corresponds to 0.70 site/polypeptide chain; and there are reasons to believe that the value of the stoichiometry may be one site per functional transporter polypeptide. The complete amino acid composition and the N- and C-terminal residues of the transporter have been determined. Both the intact transporter and transporter that had been partially depleted of carbohydrate by treatment with endo-beta-galactosidase were found to migrate anomalously upon sodium dodecyl sulfate--polyacrylamide gel electrophoresis, relative to the behavior of standard proteins.