Phlorizin binding to bilayer vesicles of phospholipids and phospholipid-cholerterol

Phlorizin inhibits sugar transport in kidney, intestine, and erythrocytes. In erythroeytes, it also inhibits anion exchange and increases anion conductance. However, the mechanism of its interaction with cell membranes is unclear. In renal cell membranes, phlorizin was found to bind not only to a specific, high-affinity protein receptor, but also to low-affinity sites of unknown nature, possibly including lipid. In this context, it seemed useful to study the binding of phlorizin to sonicated bilayer vesicles of phospholipids and phospholipid-cholesterol

Localization and characterization of transport-related elements in the plasma membrane of turtle bladder epithelial cells

A mixed membrane preparation obtained from turtle bladder epithelial cells contains (Na+ + K+)-ATPase, adenylate cyclase and protein kinase, which interact with ouabain, norepinephrine and cyclic AMP, respectively. When such a preparation is obtained from bladders which had been preexposed to serosal fluids containing the tritiated form of 4,4′-diisothiocyano-2,2′-disulfonic stilbene, the subsequently isolated membrane proteins are enriched in tritium as well as in the afore-mentioned enzymes, none of which is inhibited. Freeflow electrophoresis separates the mixed membrane preparation into two distinguishable groups: one, construed as apical membranes, is enriched in norepinephrine-sensitive adenylate cyclase and cyclic AMP-sensitive protein kinase; the other, construed as basal-lateral membranes, is enriched in ouabain-sensitive ATPase and 4,4′-diisothiocyano-2,2′-disulfonic stilbene-binding proteins. The physiological counterparts of these enzymatically defined membrane markers are the mucosal sidedness of the transport effects of norepinephrine and cyclic AMP derivatives and the serosal sidedness of the transport effects of ouabain and disulfonic stilbenes in the intact turtle bladder. The discreteness and ion selectivity of each membrane-bound, transport-related element are discussed in relation to the corresponding characteristics of each transport process in vivo; the possibility of regulation of anion transport by adenylate cyclase-protein kinase system is also discussed