Biomaterial Database

Combined effects of ATP and phosphate on rubidium exchange mediated by Na-K-ATPase reconstituted into phospholipid vesicles. 1982

S J Karlish, and W R Lieb, and W D Stein

1. Phospholipid vesicles reconstituted with Na-K-ATPase show an (ATP+phosphate)-stimulated Rb-Rb exchange, with properties similar to the K-K exchange of human red cells. This includes a rate 15-20% of the rate of active ATP-dependent Na-K exchange.2. We have studied activation of this Rb-Rb exchange by ATP at fixed phosphate concentrations and by phosphate at fixed ATP concentrations. It is found for both ATP and phosphate that with low concentrations of the fixed ligand an increase in concentration of the complementary ligand produces first stimulation and then inhibition of Rb-Rb exchange. At high concentrations of the fixed ligand the complementary ligand shows only saturation behaviour.3. The pattern of activation and of inhibition by ATP and by phosphate is affected by the Rb(0) concentration in the exterior medium, in that higher concentrations of Rb(0) counteract inhibitory effects of high concentrations of ATP and phosphate.4. (ATP+phosphate)-stimulated Rb-Rb exchange is activated by Rb(0) in the exterior medium along a sigmoid curve. An increase of Rb(i) within the vesicles, which raises the maximal velocity of Rb-Rb exchange, is accompanied by a smaller increase in the Rb(0) concentration required for half-maximal stimulation of the Rb-Rb exchange.5. The data are interpreted in terms of a model similar to those proposed by Karlish & Stein (1982a,b), but extended to include simultaneous effects of ATP and phosphate. Inhibitions by high concentration of ATP or phosphate arise as a result of stabilization of E(1) ATP or E(2)-P forms respectively, in the presence of low concentrations of the complementary ligand. With high concentrations of the fixed ligand, saturation behaviour of the varying ligand is observed because the occluded Rb forms become the dominant transport intermediates. The occluded Rb forms bind both ATP and phosphate weakly and independently. The effects of ATP together with phosphate are accounted for by a simple combination of their separate effects on the Rb-Rb exchange.6. We suggest that the functional role of the occluded Rb form E(2) (Rb)(occ) in active transport is to minimize passive cation leaks through the system and allow control of the direction of cation movements by binding of physiological ligands such as ATP or phosphate.

UI	MeSH Term	Description	Entries
D007473	Ion Channels	Gated, ion-selective glycoproteins that traverse membranes. The stimulus for ION CHANNEL GATING can be due to a variety of stimuli such as LIGANDS, a TRANSMEMBRANE POTENTIAL DIFFERENCE, mechanical deformation or through INTRACELLULAR SIGNALING PEPTIDES AND PROTEINS.	Membrane Channels,Ion Channel,Ionic Channel,Ionic Channels,Membrane Channel,Channel, Ion,Channel, Ionic,Channel, Membrane,Channels, Ion,Channels, Ionic,Channels, Membrane
D007668	Kidney	Body organ that filters blood for the secretion of URINE and that regulates ion concentrations.	Kidneys
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D010710	Phosphates	Inorganic salts of phosphoric acid.	Inorganic Phosphate,Phosphates, Inorganic,Inorganic Phosphates,Orthophosphate,Phosphate,Phosphate, Inorganic
D010743	Phospholipids	Lipids containing one or more phosphate groups, particularly those derived from either glycerol (phosphoglycerides see GLYCEROPHOSPHOLIPIDS) or sphingosine (SPHINGOLIPIDS). They are polar lipids that are of great importance for the structure and function of cell membranes and are the most abundant of membrane lipids, although not stored in large amounts in the system.	Phosphatides,Phospholipid
D000254	Sodium-Potassium-Exchanging ATPase	An enzyme that catalyzes the active transport system of sodium and potassium ions across the cell wall. Sodium and potassium ions are closely coupled with membrane ATPase which undergoes phosphorylation and dephosphorylation, thereby providing energy for transport of these ions against concentration gradients.	ATPase, Sodium, Potassium,Adenosinetriphosphatase, Sodium, Potassium,Na(+)-K(+)-Exchanging ATPase,Na(+)-K(+)-Transporting ATPase,Potassium Pump,Sodium Pump,Sodium, Potassium ATPase,Sodium, Potassium Adenosinetriphosphatase,Sodium-Potassium Pump,Adenosine Triphosphatase, Sodium, Potassium,Na(+) K(+)-Transporting ATPase,Sodium, Potassium Adenosine Triphosphatase,ATPase Sodium, Potassium,ATPase, Sodium-Potassium-Exchanging,Adenosinetriphosphatase Sodium, Potassium,Pump, Potassium,Pump, Sodium,Pump, Sodium-Potassium,Sodium Potassium Exchanging ATPase,Sodium Potassium Pump
D000255	Adenosine Triphosphate	An adenine nucleotide containing three phosphate groups esterified to the sugar moiety. In addition to its crucial roles in metabolism adenosine triphosphate is a neurotransmitter.	ATP,Adenosine Triphosphate, Calcium Salt,Adenosine Triphosphate, Chromium Salt,Adenosine Triphosphate, Magnesium Salt,Adenosine Triphosphate, Manganese Salt,Adenylpyrophosphate,CaATP,CrATP,Manganese Adenosine Triphosphate,MgATP,MnATP,ATP-MgCl2,Adenosine Triphosphate, Chromium Ammonium Salt,Adenosine Triphosphate, Magnesium Chloride,Atriphos,Chromium Adenosine Triphosphate,Cr(H2O)4 ATP,Magnesium Adenosine Triphosphate,Striadyne,ATP MgCl2
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D001693	Biological Transport, Active	The movement of materials across cell membranes and epithelial layers against an electrochemical gradient, requiring the expenditure of metabolic energy.	Active Transport,Uphill Transport,Active Biological Transport,Biologic Transport, Active,Transport, Active Biological,Active Biologic Transport,Transport, Active,Transport, Active Biologic,Transport, Uphill
D012413	Rubidium	An element that is an alkali metal. It has an atomic symbol Rb, atomic number 37, and atomic weight 85.47. It is used as a chemical reagent and in the manufacture of photoelectric cells.