Isolation of a Glucose‐Binding Lipoprotein from Yeast Plasma Membrane

Baker's yeast membranes were solubilized with Tween 80, the material was chromatographed on Sephadex G‐150 and hydroxyapatite and finally treated with ammonium sulphate and in an isopycnic gradient of sucrose, to yield a lipoprotein complex which appears homogeneous in disc electrophoresis. The complex binds d ‐glucose, d ‐xylose, d ‐arabinose, l ‐sorbose, but not d ‐galactose and l ‐arabinose, showing thus the specificity of the typical glucose carrier from baker's yeast. The binding is suppressed by dodecylsulphate and by treatment at 90°C, but not by 2,4‐dinitrophenol or N ‐ethylmaleimide. The molecular weight of the protein (per binding site) appears to be about 5000, that of the lipoprotein (from analysis of P and N) about 35000. The lipid part contains phosphatidylcholine, phosphatidylethanolamine and probably lysophosphatidylcholine. There are a minimum of 3 × 10 6 glucose‐binding sites per cell.