Studies of red cell and other membrane extracts in relation to glucose permeability

Abstract

Two possible mechanisms involved in the facilitated transfer of glucose through red cell and other membranes have been investigated. In the first section, the hypothesis that glucose transfer involves phosphorylation was tested by estimating phosphatase activities in human red cells, adult and foetal guinea-pig red cells and kidney homogenates, and the effects upon them of known inhibitors of glucose transfer. No correlation between phosphatase activity and glucose transfer in the red cell could be found. Histochemical studies are presented to show the distribution of acid and alkaline phosphatases in the adult and foetal guinea-pig kidney, and the placenta. In the second section, the possibility is explored that glucose forms a reversible complex with a phospholipid component of the cell membrane. Methods were developed to extract phospholipids from sheep placental tissue and human and sheep red cells, to separate them chromatographically and to isolate the glucose-lipid complex. Uptake of the irreversible inhibitor 2,4-dinitrofluorobenzene (DNFB) labelled with was measured, and calculated to be 400 million molecules per red cell to give full inhibition of glucose transfer. The lipids extracted from the DNFB inhibited red cells contained radioactivity equivalent to 10-20 million molecules DNFB per red cell, which considerably exceeds the number of carrier sites thought to be involved in glucose transfer. A large proportion of the radioactivity was found in the cephalin fractions, and the possibility is discussed that phosphatidyl ethanolamine is the membrane carrier component. The technique of monolayers was used to study the surface behaviour of certain phospholipids in the presence of glucose, and the preliminary results obtained were discussed.