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• W2062696348 abstract "To determine in which way the cytoplasmic phosphate potential [ATP]/[ADP] [Pi] influences the rate of the respiratory chain and ATP synthesis in pig heart mitochondria, the effects of systematic variations of ATP, ADP and H3PO4 concentrations and of the whole phosphate potential in the incubation medium have been studied simultaneously on the oxygen uptake, the respiratory control ratio and the kinetics of transformation of the nucleotides and phosphate. 1 Washing the mitochondria lowers their content of orthophosphate ATP, ADP, AMP and NAD, but does not affect their respiratory rate (states 3 and 4 according to Chance and Williams). 2 The phosphate concentration at half maximum velocity of ATP synthesis and of substrate oxidation (glutamate, α-ketoglutarate, β-hydroxybutyrate or succinate) is 200 μM (apparent Km). To obtain a typical straight line in reciprocal plots of Lineweaver and Burk 1/v against 1/[phosphate], one must take into account endogeneous as well as exogeneous phosphate. 3 The ADP concentration at half maximum velocity of oxidation of the 4 substrates (state 3) is: apparent Km between 5 to 20 μM, while it is equal to = 40 μM towards ATP synthesis during the state 3 of oxidation. The ADP/O and P/O ratios approach theoretical values, but the final yield of transformation of ADP into ATP is only 70 to 80%; this yield is independent of the initial concentration of added ADP (25 to 400 μM). 4 In the presence of Mg2+ and phosphate, the addition of ATP (0 to 1,500 μM) does not modify either the state 3 of oxidation, or the ATP synthesis; meanwhile, no specific ATPase activity takes place. However, added ATP speeds up state 4 of oxidation. In the same way, ATP, synthetized by the mitochondria after the addition of ADP, does not affect state 3 but speeds up state 4 of oxidation. Creatine additions (0 to 600 μM) do not affect the respiratory rate in the absence of ATP but the maximum acceleration produced by ATP on state 4 is increased proportionally to the quantity of added creatine. This fact is noteworthy since pig heart mitochondria creatine contents are much higher than their adenine nucleotides contents (free creatine and creatine phosphate: each 30 nmoles/mg protein). In the absence of Mg2+ and in the presence of EDTA (1 to 3 mM), the respiratory level at state 4 is lower; then, ATP (added or synthetized by the mitochondria) no longer accelerates state 4 of oxidation. 5 When orthophosphate is not limiting (5 mM), the presence of ATP (0 to 1,750 μM) does not affect the apparent Km for ADP towards the oxidative phosphorylations. This Km is thus independent of the external [ATP]/[ADP] [Pi] ratio. 6 The kinetics of transformation of the nucleotides added to the mitochondria have been studied. The nucleotides were estimated by chromatography or by enzymatic methods, which gave identical results. A simultaneous formation of ATP and AMP immediately follows the addition of ADP to mitochondria (400 nmoles/3 mg proteins). After ten seconds, the level of AMP is maximum (80 nmoles/3 mg proteins) then it goes down to zero while the ATP synthesis rate is lowered. The kinetics of nucleotide evolution are of the same type during the oxidation of the four substrates and whether pig heart or rat liver mitochondria are concerned. If ATP is added instead of ADP, the nucleotides distribution is not modified. In the presence of oligomycin, the added ADP is converted into an equimolecular mixture of ATP and AMP until the equilibrium of the reaction 2 ADP ⇄ AMP + ATP (K= 0.68 at 28°) is reached. In the presence of 2,4-dinitrophenol the same equilibrium is reached and the ATP formed is only slightly hydrolysed. In the absence of Mg2+ and in the presence of EDTA, the ATP synthesis is a sigmoïdal function of the time and there is no formation of AMP. The kinetics of 32mP incorporation into ATP in the presence of Mg2+ fits with the production of ATP in the absence of Mg2+ but in the presence of EDTA. 7 The results allow a comparison of the affinity of the various enzymatic systems towards ADP. Mg2+ being present, apparent Km (ADP) for the oxidation rate is between 5 to 20 μM while the apparent Km= 40 pM for the ATP synthesis; in the presence of EDTA, Km (ADP) = 50 μM for the ATP synthesis; in the presence of oligomycin apparent Km (ADP) = 90 pM (ATP synthesis). When both EDTA and oligomycin are added, endogeneous ATP is slightly lowered but ADP does not vary. As a general conclusion, the external phosphate potential does not represent the regulatory system for respiratory chain activity. ATP does not appear to enter but goes out easily. If the affinity of ADP towards the oxidative phosphorylations is great, its entrance speed seems to be limiting. The affinity of oxidative phosphorylations towards orthophosphate is weak but the entrance of phosphate does not seem to be limiting. Moreover, adenylate kinase, or systems of the same type, modify all the signals coming from the cytoplasm and cooperate with oxidative phosphorylations to adjust a t any moment the level of each nucleotide." @default.
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• W2062696348 date "1969-04-01" @default.
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• W2062696348 title "Regulation de l'activite respiratoire des mitochondries de coeur de porc et transformations des nucleotides adenyliques et du phosphate" @default.
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• W2062696348 doi "https://doi.org/10.1111/j.1432-1033.1969.tb00539.x" @default.
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