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Results for “OXIDATIVE PHOSPHORYLATION”

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PubMed1975

Effects of 5,5'-diphenyl-2-thiohydantoin on respiration and oxidative phosphorylation of rat liver mitochondria.

5,5'-Diphenyl-2-thiohydantoin (DPTH) administered in vitro, inhibited state 3 oxidation, stimulated state 4 oxidation and decreased ADP:O ratio when 3-hydroxybutyrate and succinate were used as substrates. Considerably lower DPTH concentrations were required for the inhibition of 3-hydroxybutyrate oxidation (50% inhibition occurred at approximately 0.17 mumoles DPTH/mg protein) than were needed for inhibition of succinate oxidation (50% inhibition occurred at about 0.62 mumoles DPTH/mg protein). DPTH showed no inhibitory effects when ascorbate plus tetramethylphenylenediamine (TMPD) served as the substrate. The inhibition of state 3 respiration was not reversed by 2,4-dinitrophenol (DNP), although there was a slight increase in the DNP rate:state 3 rate suggesting the presence of a weak DPTH inhibotory site located within the Site I energy transport chain. Uncoupling, in the presence of DPTH, was observed with all substrates. In experiments utilizing sonicated mitochondria, DPTH inhibited NADH-linked oxidation, but did not inhibit succinate or ascorbate plus TMPD oxidation. The effects of DPTH were reversed by dilution and by addition of albumin. DPTH concentrations which produced inhibition of state 3 respiration in vitro were reached, in vivo, in the livers of rats receiving a single oral dose of 40 mg/kg of DPTH.

Animals↗
PubMed1993

Control of the effective P/O ratio of oxidative phosphorylation in liver mitochondria and hepatocytes.

The control exerted by substrate oxidation reactions, by ATP turnover and by the proton leak over the oxygen consumption rate, the phosphorylation rate, the proton leak rate and the protonmotive force (delta p) in isolated rat liver mitochondria under a range of conditions between non-phosphorylating (State 4) and maximum phosphorylation (State 3) was investigated by using the top-down approach of metabolic control analysis. The experiments were carried out with saturating concentrations of the substrates succinate, glutamate with malate, or pyruvate with malate. The distribution of control was very similar with each of the three substrates. The effective P/O ratio (i.e. not corrected for leak reactions) was also measured; it varied from zero in State 4 to 80-90% of the maximum theoretical P/O ratio in State 3. Under most conditions control over the effective P/O ratio was shared between proton leak (which had negative control) and the phosphorylating subsystem (which had roughly equal positive control); near State 4, substrate oxidation reactions also acquired some control over this ratio. In resting hepatocytes the effective P/O ratio was only 50% of its maximum theoretical value, corresponding to an effective P/O ratio of only 1.3 for complete oxidation of glucose. The effective P/O ratio for intracellular mitochondrial oxygen consumption was 64% of the maximum value. The control coefficient of the mitochondrial proton leak over the effective P/O ratio in cells was -0.34; the control coefficient of phosphorylation reactions over this ratio was 0.31 and the control coefficient of substrate oxidation reactions over the ratio was 0.03, showing how the coupling efficiency in cells can respond sensitively to agents that change the proton leak or the ATP demand, but not to those that change substrate oxidation.

Adenosine Triphosphate↗