Reversal of oxidative phosphorylation in submitochondrial particles using glucose 6-phosphate and hexokinase as an ATP regenerating system.
During steady-state, the Pi released in the medium is derived from glucose-6-phosphate which continuously regenerates the ATP hydrolyzed. A membrane potential (delta psi) can be built up in submitochondrial particles using glucose-6-phosphate and hexokinase as an ATP-regenerating system. The energy derived from the membrane potential thus formed, can be used to promote the energy-dependent transhydrogenation from NADH to NADP+ and the uphill electron transfer from succinate to NAD+. In spite of the large differences in the energies of hydrolysis of ATP (delta G degrees = -7.0 to -9.0 kcal/mol) and of glucose-6-phosphate (delta G degrees = -2.5 kcal/mol), the same ratio between Pi production and either NADPH or NADH formation were measured regardless of whether millimolar concentrations of ATP or a mixture of ADP, glucose-6-phosphate and hexokinase were used. Rat liver mitochondria were able to accumulate Ca2+ when incubated in a medium containing hexokinase, ADP and glucose-6-phosphate. The different reaction measured with the use of glucose-6-phosphate and hexokinase were inhibited by glucose concentrations varying from 0.2 to 2 mM. Glucose shifts the equilibrium of the reaction towards glucose-6-phosphate formation thus leading to a decrease of the ATP concentration in the medium.
de Meis
L
L
Departamento de Bioquímica, Universidade Federal do Rio de Janeiro, Cidade Universitária, Ilha do Fundão, Brazil.
Grieco
M A
MA
Galina
A
A
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002413:Cations, Divalent; D002417:Cattle; D004579:Electron Transport; D005958:Glucosephosphates / Q000378:metabolism*; D006593:Hexokinase / Q000378:metabolism*; D006868:Hydrolysis; D007425:Intracellular Membranes / Q000502:physiology; D008564:Membrane Potentials; D008929:Mitochondria, Heart / Q000648:ultrastructure; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010085:Oxidative Phosphorylation; D013367:Submitochondrial Particles / Q000378:metabolism*
D002413:Cations, Divalent; D005958:Glucosephosphates; D009243:NAD; D009249:NADP; D000255:Adenosine Triphosphate; D006593:Hexokinase; D002118:Calcium