mersalyl and malic-acid

To date, the existence of the plant inner membrane anion channel (PIMAC) has been shown only in potato mitochondria, but its physiological role remains unclear. In this study, by means of swelling experiments in K(+) and ammonium salts, we characterize a PIMAC-like anion-conducting pathway in mitochondria from durum wheat (DWM), a monocotyledonous species phylogenetically far from potato. DWM were investigated since they possess a very active potassium channel (PmitoK(ATP)), so implying a very active matching anion uniport pathway and, possibly, a coordinated function. As in potato mitochondria, the electrophoretic uptake of chloride and succinate was inhibited by matrix [H(+)], propranolol, and tributyltin, and was insensitive to Mg(2+), N,N'-dicyclohexylcarbodiimide (DCCD) and mercurials, thus showing PIMAC's existence in DWM. PIMAC actively transports dicarboxylates, oxodicarboxylates, tricarboxylates and Pi. Interestingly, a novel mechanism of swelling in ammonium salts of isolated plant mitochondria is reported, based on electrophoretic anion uptake via PIMAC and ammonium uniport via PmitoK(ATP). PIMAC is inhibited by physiological compounds, such as ATP and free fatty acids, by high electrical membrane potential (Delta Psi), but not by acyl-CoAs or reactive oxygen species. PIMAC was found to cooperate with dicarboxylate carrier by allowing succinate uptake that triggers succinate/malate exchange in isolated DWM. Similar results were obtained using mitochondria from the dicotyledonous species topinambur, so suggesting generalization of results. We propose that PIMAC is normally inactive in vivo due to ATP and Delta Psi inhibition, but activation may occur in mitochondria de-energized by PmitoK(ATP) (or other dissipative systems) to replace or integrate the operation of classical anion carriers.

Topics: Adenosine Triphosphate; Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; Fatty Acids; Helianthus; Hydrogen Peroxide; Hydrogen-Ion Concentration; Ion Channels; Linoleic Acid; Malates; Membrane Potential, Mitochondrial; Mersalyl; Mitochondria; Mitochondrial Membranes; Mitochondrial Swelling; NAD; Osmosis; Propranolol; Solutions; Succinic Acid; Superoxides; Triticum

Ornithine uptake by rat kidney mitochondria is here first shown by monitoring the reduction of the intramitochondrial pyridine nucleotides which occurs as a result of metabolism of imported ornithine via ornithine aminotransferase and 1-pyrroline-carboxylate dehydrogenase. Ornithine uptake shows saturation features (Km and Vmax values, measured at 20 degrees C and at pH 7.20, were found to be about 0.85 mM and 23 nmoles/min x mg protein, respectively) and proves to be inhibited by D-ornithine, inorganic phosphate, praseodimium chloride and mersalyl. Neither malate nor glutamate, but phosphate was found to exchange with ornithine. Phosphate efflux caused by externally added ornithine was shown both as revealed by a c colorimetric assay and as continuously monitored by measuring extramitochondrial reduction of NAD+ in the presence of glyceraldehyde-3-phosphate, glyceraldehyde-3-phosphate dehydrogenase, ADP and 3-phosphoglycerate kinase. The role of ornithine carrier in kidney metabolism will also be discussed.

Topics: Animals; Biological Transport; Carrier Proteins; Fluorometry; Glutamates; Glutamic Acid; Kidney; Kinetics; Malates; Male; Membrane Transport Proteins; Mersalyl; Mitochondria; NAD; NADP; Ornithine; Oxidation-Reduction; Phosphates; Praseodymium; Rats; Rats, Inbred Strains; Spectrophotometry

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

Reconstruction, using non-synaptosomal rat brain mitochondria, has been made here of the malate/oxaloacetate shuttle, made possible by the occurrence in rat brain mitochondria of a carrier mediated transport for oxaloacetate (Km = 60 microM), sensitive to dicarboxylate analogues and mersalyl, and of the two isoenzymes of malate dehydrogenase. Malate/oxaloacetate shuttle shows a high affinity for malate (Km = 100 microM) and Vmax = 40 nmoles NADH oxidized/min X mg mitochondrial protein at 20 degrees C. Its rate appears to depend on the activity of the malate/oxaloacetate exchange across the mitochondrial membrane. A possible role for the oxaloacetate carrier is proposed in aminoacid brain metabolism.

Topics: Animals; Biological Transport; Brain; Kinetics; Malates; Mersalyl; Mitochondria; Oxaloacetates; Oxidation-Reduction; Rats