Binding of radioactively labeled carboxyatractyloside, atractyloside and bongkrekic acid to the ADP translocator of potato mitochondria

1. The inhibition of the ADP-stimulated respiration of potato mitochondria by carboxyatractyloside is relieved by high concentration of ADP or by the uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP). Atractyloside is a much less potent inhibitor than carboxyatractyloside. The inhibition of the ADP-stimulated respiration required about 60-times more atractyloside than carboxyatractyloside. 2. [35S]carboxyatractyloside and [3H]bongkrekic acid bind to potato mitochondria with high affinity (Kd = 10 to 20 nM, n=0.6-0.7 nmol per mg protein). Added ADP competes with carboxyatractyloside for binding; on the contrary ADP increases the amount of bound bongkrekic acid. [3H]atractyloside binds to potato mitochondria with a much lower affinity (Kd=0.45 muM) than carboxyatractyloside or bongkrekic acid. 3. Bound [3H]atractyloside is displaced by ADP, carboxyatractyloside and bongkrekic acid. The displacement of bound [35S]carboxyatractyloside by bongkrekic acid and of bound [3H]bongkrekic acid by carboxyatractyloside is markedly increased by ADP. 4. Bongkrekic acid competes with [35S]carboxyatractyloside for binding. Addition of a small concentration of ADP considerably enhances the inhibitory effect of bongkrekic acid on [35S]carboxyatractyloside binding. 5. The adenine nucleotide content of potato mitochondria is of the order of 1 nmol per mg protein. ADP transport in potato mitochondria is inhibited by atractyloside 30- to 40-times less efficiently than by carboxyatractyloside.

Isobongkrekic acid, a new inhibitor of mitochondrial ADP-ATP transport: radioactive labeling and chemical and biological properties

An isomer of bongkrekic acid, designated as isobongkrekic acid, has been isolated from ethereal extracts of Pseudomonas cocovenenans grown on defatted coconut. Isobongkrekic acid was also obtained by alkaline treatment of bongkrekic acid. Isobongkrekic acid possesses the same ultraviolet spectrum and the same molecular weight as bongkrekic acid; it has a similar infrared spectrum but not the same nuclear magnetic resonance (NMR) spectrum. The differences in NMR data were interpreted to mean that isobongkrekic acid differs from bongkrekic acid by the configuration of the dicarboxylic end; whereas the two carboxylic groups of the dicarboxylic end have the trans configuration in bongkrekic acid, they have the cis configuration in isobongkrekic acid. Differences between bongkrekic and isobongkrekic acids are lost after catalytic hydrogenation of the molecules. Isobongkrekic acid, like bongkrekic acid, is an uncompetitive inhibitor of ADP transport in mitochondria, provided the mitochondria are preincubated in the presence of the inhibitor and a minute concentration of ADP. The inhibitory and binding efficiency of isobongkrekic acid is considerably increased below pH 7. The number of high affinity sites for [3H] isobongkrekic acid is 0.13 to 0.20 nmol/mg protein in rat liver mitochondria and about 1 nmol/mg protein in rat heart mitochondria, i.e., similar to the number of high affinity sites for [3H] bongkrekic acid. Isobongkrekic and bongkrekic acids compete for the same site, but the affinity of isobongkrekic acid for mitochondria is one-half to one-fourth that of bongkrekic acid.

The state of ADP or ATP fixed to the mitochondria by bongkrekate

The reported studies are intended to clarify the binding state of ADP fixed to mitochondria under the influence of bongkrekate, and thus to discern between the affinity increase and reorientation mechanism proposed for the bongkrekate effect. (a) The composition of the intramitochondrial adenine nucleotide pool is not changed under the influence of bongkrekate with and without added nucleotides. (b) The added ADP and ATP fixed by bongkrekate can be identified as AMP, ADP and ATP in the same proportions as in the endogenous pool. (c) The bound nucleotides respond to oxidative phosphorylation or uncoupler stimulated dephosphorylation similar as endogenous nucleotides. It can be concluded that the ADP or ATP fixed under the influence of bongkrekate to the mitochondria are equilibrated with the intramitochondrial adenine nucleotide pool and are active in intramitochondrial phosphate transfer reactions. The results disagree with the affinity increase mechanism but support the reorientation mechanism which postulates that ADP and ATP are trapped in the mitochondria under the influence of bongkrekate in the same amount as there are carrier sites available outside before bongkrekate addition.

Mode of stimulation by aldosterone of the sodium efflux in barnacle muscle fibres: effects of ouabain, ethacrynic acid, diphenylhydantoin, (ATPMg)(2-), adenine translocase inhibitors, pyruvate and oxythiamine

1. A study has been made of the nature of the delayed stimulation caused by external aldosterone in barnacle fibres pre-exposed to aldosterone. 2. (i) Microinjection of 0-5 M-ATPMg2- caused only a small but prompt rise in the Na efflux. (ii) Microinjection of 0-5 M-ATPMg2- followed by external application of 10(-5)M aldosterone greatly augmented the magnitude of the delayed stimulation. The response was dose-dependent, as well as dependent on the concentration of external K+ and H+, but not Na+, Ca2+ or Mg2+. (iii) External application of 10(-5) M aldosterone for 30 min followed by its withdrawal from the bathing medium failed to bring about delayed stimulation. By contrast, fibres into which ATP had been injected showed delayed stimulation under these conditions. 3. Microinjection of actinomycin-D or spironolactone SC-14266 into fibres into which ATP had been injected followed by external application of aldosterone resulted in complete abolition of the delayed stimulation. 4. Delayed stimulation was reduced whether ATP had been injected or not by prior external application of 10(-4)M ouabain or internal application of 8 x 10(-2)M ethacrynic acid. It was completely abolished by prior application of ouabain externally and ethacrynic acid internally, or only 10(-4)M diphenylhydantoin externally. 5. (i) Microinjection of atractyloside or bongkrekic acid caused a substantial fall in the resting Na efflux. Bonkrekic acid proved more powerful than atractyloside. Microinjection of 0-05 M-ATPMg2- into fibres poisoned with 2-0 x 10(-2)M bongkrekic acid completely restored the Na efflux.

Rickettsial permeability. An ADP-ATP transport system

The obligate intracellular parasitic bacterium, Rickettsia prowazeki, has a carrier-mediated transport system for ADP and ATP. The transport of nucleotides was measured by membrane filtration assays; the assay was shown not to harm the relatively labile rickettsiae. The nucleotide transport system was shown to reside in the rickettsiae, not in the contaminating yolk sac mitochondria of the preparation. The influx of nucleotide had an activation energy of 12 to 13 kcal above 22 deg-rees (an apparent transition temperature), and 30 kcal below this value. The uptake of nucleotide was independent of the Mg2+ concentration, but was markedly stimulated by the phosphate concentration. The pH optimum of the influx of nucleotide was pH 7. The specificity of the transport system was remarkable in that it required a specific moiety in each portion of the nucleotide, i.e. an adenine base, a ribose sugar, and two or three, but not one, phosphates. Of the wide variety of compounds tested, the system could transport only ADP, ATP, and (beta, gamma-methylene) adenosine 5'-triphosphate. The influx of nucleotide was a saturable process; half-maximum velocity was achieved at a nucleotide concentration of about 75 muM. ADP and ATP were competitive inhibitors of each other's transport. Although at least 95% of the labeled intracellular nucleotide was exchangeable, efflux of labeled nucleotide was observed only in the presence of unlabeled nucleotide in the medium. Half-maximum efflux was achieved at a concentration of about 75 muM. A large intracellular to extracellular concentration gradient of labeled nucleotide was maintained in the presence of metabolic inhibitors and uncouplers, which completely abolished rickettsial hemolysis. While having no effect on the steady state, KCN and DNP accelerated both influx and efflux. Measurements of the endogenous pool of adenine nucleotides in isolated rickettsiae show that is was large (5 mM), and that these unlabeled nucleotides exchanged, on approximately a 1/1 basis, with exogenously added nucleotide. These studies support the proposal that rickettsiae are not "leaky" to adenine nucleotides or to small molecules in general, and that they have a carrier-mediated transport system which allows an exchange of host and parasite ADP and ATP.

The activation of non-phosphorylating electron transport by adenine nucleotides in Jerusalem-artichoke (Helianthus tuberosus) mitochondria

In isolated plant mitochondria the oxidation of both succinate and exogenous NADH responded in the expected manner to the addition of ADP or uncoupling agents, and the uncoupled rate of respiration was often in excess of the rate obtained in the presence of ADP. However, the oxidation of NAD+-linked substrates responded in a much more complex manner to the addition of ADP or uncoupling agents such as carbonyl cyanide p-trifluoromethoxyphenylhydrazone to mitochondria oxidizing pyruvate plus malate failed to result in a reliable stimulation; this uncoupled rate could be stimulated by adding AMP or ADP in the presence of oligomycin or bongkrekic acid. Spectrophometric measurements showed that the addition of AMP or ADP resulted in the simultaneous oxidation of endogenous nicotinamide nucleotide and the reduction of cytochrome b. ADP was only effective in bringing about these changes in redox state in the presence of Mg2+ whereas AMP did not require Mg2+. It was concluded that AMP activated the flow of electrons from endogenous nicotinamide nucleotide to cytochrome b, possible at the level of the internal NADH dehydrogenase.

The binding of atractylate and carboxy-atractylate to mitochondria

35S-labelled atractylate and carboxy-atractylate are produced biosynthetically and used for studying the binding of these specific ligands to the ADP, ATP carrier in beef heart mitochondria. The following results are obtained. 1. Inhibition of translocation activity goes parallel to the increase of binding by [35S]atractylate. No additional binding is observed after full inhibition of translocation is reached giving evidence that atractylate binds exclusively to the carrier. 2. The maximum number of binding sites of both atractylates is about 1.6 mumol/g protein in beef heart mitochondria and decreases on treatment of the membrane by Pi, freezing, ageing, etc. The dissociation constants of the binding are approximately for atractylate Kd = 5-10(-8) M and for carboxy-atractylate Kd = 10(-8) M. The mass action plots of the concentration dependence for the binding are nonlinear-convex in particular with carboxy-atractylate and more linear with atractylate. Nonlinearity appears to be caused by some retardation of equilibration in the case of very high affinity binding. 3. The binding of atractylate and carboxy-atractylate is relatively fast in intact mitochondria and slower in aged membranes. There is a slower and a faster binding portion. 4. The atractylates remove ADP in a nearly 1:1 stoichiometry from untreated mitochondria. In aged and Pi-treated membranes the ratio deltaADP/deltaatractylate approaches 0. Obviously binding of carrier sites to ADP is more sensitive to alterations than that of the atractylates. The assumption is maintained that the binding site for atractylate is identical with that for ADP and ATP. 5. Bongkrekate prevents binding of both atractylates. However, when added after, it only removes atractylate but not the carboxy compound because of its different tight binding. The removal of atractylate depends on the synergistic effect of bongkrekate with ADP. 6. The binding studies with [35S]atractylate and in particular the interaction with bongkrekate support the reorienting carrier model in which atractylate as an impermeable ligand fixes the binding site of the carrier outside while with bongkrekate the carrier site is turned to the inside.