mersalyl and 2-phenylsuccinate

In order to gain a first insight into the effects of reactive oxygen species (ROS) on plant mitochondria, we studied the effect of the ROS producing system consisting of xanthine plus xanthine oxidase on the rate of membrane potential (DeltaPsi) generation due to either succinate or NADH addition to durum wheat mitochondria as monitored by safranin fluorescence. We show that the early ROS production inhibits the succinate-dependent, but not the NADH-dependent, DeltaPsi generation and oxygen uptake. This inhibition appears to depend on the impairment of mitochondrial permeability to succinate. It does not involve mitochondrial thiol groups sensitive to either mersalyl or N-ethylmaleimide and might involve both protein residues and/or membrane lipids, as suggested by the mixed nature. We propose that, during oxidative stress, early generation of ROS can affect plant mitochondria by impairing metabolite transport, thus preventing further substrate oxidation, DeltaPsi generation and consequent large-scale ROS production.

Topics: Kinetics; Membrane Potentials; Mersalyl; Mitochondria; Models, Biological; NAD; Oxidative Stress; Reactive Oxygen Species; Succinates; Succinic Acid; Triticum; Xanthine; Xanthine Oxidase

In this study we have investigated hydroxyproline transport in rat heart mitochondria and, in particular, in heart left ventricle mitochondria isolated from both spontaneously hypertensive and Wistar-Kyoto rats. Hydroxyproline uptake by mitochondria, where its catabolism takes place, occurs via a carrier-mediated process as demonstrated by the occurrence of both saturation kinetics and the inhibition shown by phenylsuccinate and the thiol reagent mersalyl. In any case, hydroxyproline transport was found to limit the rate of mitochondrial hydroxyproline catabolism. A significant change in Vmax and Km values was found in mitochondria from hypertensive/hypertrophied rats in which the Km value decreases and the Vmax value increases with respect to normotensive rats, thus accounting for the increase of hydroxyproline metabolism due to its increased concentration in a hypertrophic/hypertensive state.

Topics: Animals; Biological Transport; Heart Ventricles; Hydroxyproline; Hypertension; Intracellular Membranes; Kinetics; Male; Mersalyl; Mitochondria, Heart; NADP; Oxidation-Reduction; Rats; Rats, Inbred WKY; Succinates

Upon the addition of inorganic phosphate, isolated rat-heart mitochondria released endogenous adenine nucleotides. To elucidate the mechanism of this phosphate-induced efflux, we evaluated the relative roles of three inner mitochondrial membrane carriers: the adenine nucleotide translocase, the phosphate/hydroxyl exchanger, and the dicarboxylate carrier. Atractyloside (a specific inhibitor of the adenine nucleotide translocase) prevented this efflux, but did not inhibit mitochondrial swelling. Inhibitors of the phosphate/hydroxyl exchanger (200 microM n-ethylmaleimide and 10 microM mersalyl) did not inhibit phosphate-induced efflux. 200 microM mersalyl (which inhibited both the phosphate/hydroxyl exchanger and the dicarboxylate carrier) inhibited the rate of efflux approx. 65% Phenylsuccinate and 2-n-butylmalonate (inhibitors of the dicarboxylate carrier) partially inhibited phosphate-induced efflux and adenine nucleotide translocase activity. Mersalyl (200 microM) had no effect on adenine nucleotide translocase activity. Partial inhibition of the adenine nucleotide translocase by phenylsuccinate and butylmalonate could not explain the extent of inhibition of phosphate-efflux by these agents. Moreover, the rates of adenine nucleotide efflux in the presence of phenylsuccinate, butylmalonate, or mersalyl correlated well with the ability of these agents to inhibit succinate-supported respiration. We conclude that phosphate-induced efflux of adenine nucleotides from rat heart mitochondria occurs over the adenine nucleotide translocase, and that the site of action of the phosphate is not the phosphate/hydroxyl exchanger, but is likely the dicarboxylate carrier.

Topics: Adenine Nucleotides; Animals; Atractyloside; Carrier Proteins; Dicarboxylic Acid Transporters; Ethylmaleimide; Hydroxides; Kinetics; Male; Malonates; Mersalyl; Mitochondria, Heart; Mitochondrial ADP, ATP Translocases; Oxygen Consumption; Phosphates; Rats; Rats, Inbred Strains; Succinates; Succinic Acid

Adenine nucleotide efflux from isolated rat heart mitochondria was studied. Inorganic phosphate induced efflux of adenine nucleotides from the mitochondria. This efflux was inhibited by carboxyatractyloside and atractyloside. The rate of efflux showed saturation kinetics with respect to extramitochondrial phosphate (Km, 9.5 mM). Lowering the pH from 7.4 to 6.8 had little or no effect on the rate of efflux. Deenergizing the mitochondria enhanced carboxyatractyloside-insensitive efflux, but it did not affect carboxyatractyloside-sensitive efflux. Extramitochondrial ATP (200 microM) or AMP (200 microM) prevented efflux when the phosphate concentration was 10 mM. AMP (200 microM) did not inhibit efflux when the phosphate concentration was 40 mM. Atractyloside inhibited efflux noncompetitively with respect to inorganic phosphate. Mersalyl (10 nmol/mg protein) did not inhibit efflux. Phenylsuccinate (20 mM) totally inhibited phosphate-induced efflux. The results of this study indicate that under conditions found in the ischemic heart cell (low ATP, high phosphate), adenine nucleotides may be lost from the mitochondria via the adenine nucleotide translocase. Phosphate does not induce this efflux by interacting with the translocase or the phosphate-hydroxyl carrier. The site of action of phosphate may be the dicarboxylate carrier.

Topics: Adenine Nucleotides; Adenosine Triphosphate; Animals; Atractyloside; Coronary Disease; Male; Mersalyl; Mitochondria, Heart; Phosphates; Rats; Rats, Inbred Strains; Succinates

Fumarate permeation in isolated rat liver mitochondria was demonstrated by measuring malate and phosphate efflux caused by fumarate added externally to the mitochondrial suspension. The existence of two specific fumarate translocators, fumarate/malate and fumarate/phosphate, is shown here. These carriers are distinguished in the light of different kinetic parameters (Km values are 50 microM and 150 microM, and Vmax values are 17 and 40 nmoles/min X mg mitochondrial protein, respectively) and of differing sensitivity to non-penetrant compounds. Fumarate was found to cause oxaloacetate efflux from mitochondria by means of an indirect process which involves the cooperation of both fumarate/malate and malate/oxaloacetate translocators. Results are discussed in the light of the physiological role played by fumarate translocation in both ureogenesis and aminoacid metabolism.

Topics: Animals; Biological Transport, Active; Citric Acid Cycle; Ethylmaleimide; Fumarates; Kinetics; Malates; Malonates; Mersalyl; Mitochondria, Liver; Models, Biological; Phosphates; Rats; Succinates