Molecular Characteristics of Rat Brain Glucose Transporter: A Novel Species with Mr 45,0001

The glucose transporter of rat brain was examined by the use of cytochalasin B, a potent inhibitor. The dissociation constants (Kt) of D-glucose-inhibitable cyto-chalasin B binding in various membrane fractions were about 100 nM. Solubiliza-tion and partial purification of glucose transporter were carried out by procedures of DE 52 column chromatography, Bio Gel HT column chromatography and Se-pharose CL-6B column chromatography from postnuclear membrane fraction. Purified transporter, reconstituted in lipid vesicles, showed D-glucose-specific trans-port activity with a Michaelis constant (Km) of 7 mM. The molecular weight was estimated to be about 200K by gel filtration in the presence of 0.1 % Triton X-100. The subunit molecular weight was estimated to be 45K by SDS-polyacrylamide gel electrophoresis after photoaffinity labeling using pHJcytochalasin B as a covalent probe, indicating that rat brain glucose transporter is a tetramer. The brain utilizes glucose exclusively as an energy source and the normal functions of the brain crucially depend on the continuous supply of glu-cose from the blood stream. The entry of glucose into brain cells from the blood was reported to be mediated by a carrier protein {1-5), but few studies have been reported so far on the mechanism of glucose transport