Biomaterial Database

Energetic coupling of Na-glucose cotransport. 1991

J J Centelles, and R K Kinne, and E Heinz

Max-Planck-Institut für Systemphysiologie, Dortmund, F.R.G.

(1) Energetic coupling in Na-linked glucose transport in renal brush border membrane vesicles has been studied in terms of various carrier models differing with respect to reaction order (random vs. ordered), and to rate limitation of steps within the routes of carrier-mediated solute transfer (translation across the membrane barrier vs. binding/release between carrier and bulk solution). (2) By computer simulation it was found that effective energetic coupling requires the leakage routes to be significantly, if not predominantly, rate-limited by their (barrier-crossing) translatory steps. This does not apply to the transfer route of the ternary complex, as coupling is possible whether or not this route is rate-limited by the translatory step. (3) The system transports glucose in the absence of Na+ (uniport) and the unidirectional flux is stimulated by unlabeled glucose on the trans side (negative tracer coupling). It is concluded that glucose binds to the carrier on either side without Na, as would be consistent with either a random system or one mode of ordered system with mirror symmetry (glucose binds before Na) but inconsistent with either mode of glide symmetry. The tracer coupling appears to indicate that the rate coefficient of carrier-mediated glucose transfer exceeds that of the empty carrier. (4) The Na-linked zero-trans flow of glucose in either direction is strongly trans-inhibited by Na. This consistent with a random system in which Na blocks or retards the translocation of the glucose-free carrier, thereby reducing 'slipping' through an internal leakage route. It is also consistent with the above mentioned ordered system, (i.e., in the absence of Na-transport without D-glucose) if it is assumed that trans Na interferes with the dissociation of the ternary complex, thereby slowing the release of glucose. (5) Minimum equilibrium exchange of glucose is stimulated in the presence of Na. This appears to indicate that Na expands the flow density of carrier-mediated glucose transfer. This expansion does not result from a 'velocity effect' (the ternary complex moving faster than the binary glucose carrier complex), as Na fails to stimulate maximum equilibrium exchange. It can instead be accounted for by an 'affinity effect' (the affinity of the carrier for glucose being increased by Na) as Na depresses the Michaelis constant of equilibrium exchange.(ABSTRACT TRUNCATED AT 400 WORDS)

UI	MeSH Term	Description	Entries
D007672	Kidney Cortex	The outer zone of the KIDNEY, beneath the capsule, consisting of KIDNEY GLOMERULUS; KIDNEY TUBULES, DISTAL; and KIDNEY TUBULES, PROXIMAL.	Cortex, Kidney
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008871	Microvilli	Minute projections of cell membranes which greatly increase the surface area of the cell.	Brush Border,Striated Border,Border, Brush,Border, Striated,Borders, Brush,Borders, Striated,Brush Borders,Microvillus,Striated Borders
D008954	Models, Biological	Theoretical representations that simulate the behavior or activity of biological processes or diseases. For disease models in living animals, DISEASE MODELS, ANIMAL is available. Biological models include the use of mathematical equations, computers, and other electronic equipment.	Biological Model,Biological Models,Model, Biological,Models, Biologic,Biologic Model,Biologic Models,Model, Biologic
D009004	Monosaccharide Transport Proteins	A large group of membrane transport proteins that shuttle MONOSACCHARIDES across CELL MEMBRANES.	Hexose Transport Proteins,Band 4.5 Preactin,Erythrocyte Band 4.5 Protein,Glucose Transport-Inducing Protein,Hexose Transporter,4.5 Preactin, Band,Glucose Transport Inducing Protein,Preactin, Band 4.5,Proteins, Monosaccharide Transport,Transport Proteins, Hexose,Transport Proteins, Monosaccharide,Transport-Inducing Protein, Glucose
D003198	Computer Simulation	Computer-based representation of physical systems and phenomena such as chemical processes.	Computational Modeling,Computational Modelling,Computer Models,In silico Modeling,In silico Models,In silico Simulation,Models, Computer,Computerized Models,Computer Model,Computer Simulations,Computerized Model,In silico Model,Model, Computer,Model, Computerized,Model, In silico,Modeling, Computational,Modeling, In silico,Modelling, Computational,Simulation, Computer,Simulation, In silico,Simulations, Computer
D004734	Energy Metabolism	The chemical reactions involved in the production and utilization of various forms of energy in cells.	Bioenergetics,Energy Expenditure,Bioenergetic,Energy Expenditures,Energy Metabolisms,Expenditure, Energy,Expenditures, Energy,Metabolism, Energy,Metabolisms, Energy
D005947	Glucose	A primary source of energy for living organisms. It is naturally occurring and is found in fruits and other parts of plants in its free state. It is used therapeutically in fluid and nutrient replacement.	Dextrose,Anhydrous Dextrose,D-Glucose,Glucose Monohydrate,Glucose, (DL)-Isomer,Glucose, (alpha-D)-Isomer,Glucose, (beta-D)-Isomer,D Glucose,Dextrose, Anhydrous,Monohydrate, Glucose
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