title: Reconstruction of steady state in cell-free systems. Interactions between glycolysis and mitochondrial metabolism: regulation of the redox and phosphorylation states.
abstract: A reconstituted "open" system comprising respiring mitochondria and actively glycolyzing muscle extract was devised for studies of vectorially mediated interactions. Glycogen particles were the substrate for the glycolyzing enzymes. Purified soluble (F1) ATPase was added in varying quantities to establish a range of energetic steady states. The data generally confirm our recent conclusions (Wu and Davis, (1981) Arch. Biochem. Biophys. 208, 85-89) on the relative efficacy of the adenine nucleotides and their ratios, and of inorganic phosphate on flux through rate-controlling steps of glycolysis. When mitochondrial ATP synthesis was blocked, glycolytic flux was relatively rapid, and the lactate/pyruvate ratio increased with time to values up to greater than 300. If functional mitochondria were present, glycolytic flux was very strongly suppressed, provided the energy state (ATP/ADP) was high, and the phosphate concentration[Pi] was low. Adenine nucleotide control of glycolysis was to a large extent lost when the steady-state ATP/ADP was below about 10, or if [Pi] was elevated. In the two-phase system containing respiring mitochondria and components of the malate-aspartate shuttle, the ATP/ADP and both extra- and intramitochondrial NAD+/NADH ratios were maintained constant, and to various perturbable levels with varying energy load (ATPase). The gradient in reduction potentials attained values (delta Gredox) of up to about 2.5 kcal. The extramitochondrial redox state was not positively correlated with the external phosphorylation potential ([ATP]/[ADP] X [Pi]). The following conclusions are drawn on the basis of the present data, together with other reports (Davis, Bremer, and Akerman (1980) J. Biol. Chem. 255, 2277-2283) and (Klingenberg and Rottenberg (1977) Eur. J. Biochem. 73, 125-130): (a) the gradient in reduction potential is driven by the membrane potential (delta psi), mediated by the electrogenic glutamate-aspartate exchange, and the poise or set point of this gradient is a function of delta psi; and (b) the gradient of ATP/ADP ratios across the membrane is also driven principally by delta psi, mediated by the electrogenic ATP-ADP exchange. Hence, segregation of phosphorylation and reduction potentials is linked through a mutually shared electrical driving force.
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002417:Cattle; D002474:Cell-Free System; D055598:Chemical Phenomena; D002621:Chemistry; D002625:Chemistry, Organic; D003600:Cytosol / Q000378:metabolism; D006019:Glycolysis; D008297:Male; D008928:Mitochondria / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D055601:Organic Chemistry Phenomena; D010084:Oxidation-Reduction; D010766:Phosphorylation; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D009243:NAD; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases