The effect of agaric acid on citrate transport in rat liver mitochondria

Antimicrobial activity and cytotoxicity of transition metal carboxylates derived from agaric acid

Carboxylato-type transition metal complexes with agaric acid, a bioactive natural compound derived from citric acid, were prepared, and tested in vitro for their antimicrobial activity and cytotoxicity. The products as well as agaric acid itself are amphiphilic compounds containing a hydrophilic head (citric acid moiety) and a hydrophobic tail (non-polar alkyl chain). The putative composition of the carboxylates was assigned on grounds of elemental analysis, infrared (IR) and high-resolution mass spectra (HR-MS), as well as in analogy with known complexes containing the citrate moiety. The metal carboxylates showed interesting activity in several microbial strains, especially against S. aureus (vanadium complex; MIC = 0.05 mg/ml). They were also tested for their cytotoxic activity in hepatocytes, the highest activity having been found in the copper(II) and manganese(II) complexes. Further research based on these preliminary results is needed in order to evaluate the influence of parameters like stability of the metal complexes in solution on the bioactivity of the complexes.

Biochemical effects of gossypol in isolated mitochondria: monovalent cations and ATPase activity

1. The effect of gossypol acetic acid upon the energy-producing system of isolated liver mitochondria was studied. Gossypol was found to exert an uncoupling effect. 2. Oxygen consumption and ATPase activity were stimulated only when a monovalent alkali metal cations was present. 3. The mitochondrial proton gradient, produced by the enzymatic hydrolysis of ATP, was lower in the gossypol-treated mitochondria than in the control experiments. 4. It is proposed that gossypol stimulates oxygen consumption and the ATPase activity in mitochondria by a protonophoretic effect and a cation translocation process.

Metabolite transport in mitochondria as a function of osmolarity

The effect of increasing sucrose concentrations on some mitochondrial functions was studied. The results showed that high osmolarity inhibits oxidative phosphorylation as well as ATPase activity and ATP-dependent delta phi formation as a consequence of adenine nucleotide translocase inhibition. It is also shown that high osmolarity does not affect delta phi formation and energy-dependent Ca2+ uptake as driven by succinate oxidation. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis of membrane proteins showed a different reactivity to o-phenantroline/Cu2+ as function of osmolarity. It is proposed that high sucrose concentrations induce a collapse of the matrix compartment that results in a restricted diffusion of some metabolites.

Decreased exchange of adenine nucleotides in human placental mitochondria

The purpose of this work was to study the exchange of adenine nucleotides in mitochondria isolated from human placenta tissue. The results indicate that ADP and ATP are translocated at a lower rate than those reported for rat liver mitochondria. It is proposed that the limited transport is due to the particular lipid composition of placental mitochondria membrane, which induces an arrest in membrane fluidity with the consequent restriction in adenine nucleotide translocase mobility.

Inhibition of mitochondrial substrate anion translocators by a synthetic amphipathic polyanion

A synthetic polyanion (a copolymer of methacrylate, maleate, and styrene in 1:2:3 proportion with an average molecular weight of 10,000 dalton) inhibits the tricarboxylate, oxoglutarate, dicarboxylate, and adenine nucleotide translocators of rat liver mitochondria. The activity versus inhibitor concentration curves are sigmoidal. The inhibition of the oxoglutarate and tricarboxylate translocators by the polyanion is competitive, while that of the adenine nucleotide translocator is of mixed-type. The K1 values of the polyanion are the following: for oxoglutarate translocator 4.0 microM, tricarboxylate translocator 1.2 microM, and adenine nucleotide translocator 1.3 microM with ADP and 0.9 microM with ATP. It is suggested that the polyanion acts primarily by increasing the negative charge of the inner membrane at the outer surface, and the sensitivity of the translocators toward the polyanion depends on the number of negative charges of their substrates.

Phosphoenolpyruvate efflux from kidney cortex mitochondria of rabbit

(1) The relationship between phosphoenolpyruvate formation and its accumulation in kidney cortex mitochondria of rabbit was studied in the presence of glutamate as substrate. (2) In mitochondria incubated in either State 4 or under uncoupled conditions, both 1,2,3-benzenetricarboxylate and atractyloside resulted in a marked elevation of the intramitochondrial phosphoenolpyruvate accompanied by a 2-4-fold decline in production of this compound. The same effect was induced by n-butylmalonate in uncoupled mitochondria, while both phosphoenolpyruvate efflux and its production were inhibited to a smaller extent in mitochondria incubated with 1,2,3-benzenetricarboxylate in State 3. (3) Citrate, malate or 2-phosphoglycerate caused a fast displacement of phosphoenolpyruvate from atractyloside-inhibited mitochondria to the reaction medium. In contrast, on the addition of ATP to mitochondria incubated with 1,2,3-benzenetricarboxylate, the rate of phosphoenolpyruvate efflux was lower than that induced by either malate or citrate. (4) Despite the presence of both 1,2,3-benzenetricarboxylate and atractyloside, arsenite and rotenone plus antimycin resulted in a leakage of phosphoenolpyruvate from the mitochondria, probably via a carrier-independent mechanism. (5) Based on the present results it seems that depending on the metabolic condition, the tricarboxylate carrier and the adenine nucleotide translocase are functioning to different extents in the efflux of phosphoenolpyruvate from rabbit renal mitochondria to the surrounding medium.