High efficiency of energy flux controls within mitochondrial interactosome in cardiac intracellular energetic units.

The aim of our study was to analyze a distribution of metabolic flux controls of all mitochondrial complexes of ATP-Synthasome and mitochondrial creatine kinase (MtCK) in situ in permeabilized cardiac cells. For this we used their specific inhibitors to measure flux control coefficients (C(vi)(JATP)) in two different systems: A) direct stimulation of respiration by ADP and B) activation of respiration by coupled MtCK reaction in the presence of MgATP and creatine. In isolated mitochondria the C(vi)(JATP) were for system A: Complex I - 0.19, Complex III - 0.06, Complex IV 0.18, adenine nucleotide translocase (ANT) - 0.11, ATP synthase - 0.01, Pi carrier - 0.20, and the sum of C(vi)(JATP) was 0.75. In the presence of 10mM creatine (system B) the C(vi)(JATP) were 0.38 for ANT and 0.80 for MtCK. In the permeabilized cardiomyocytes inhibitors had to be added in much higher final concentration, and the following values of C(vi)(JATP) were determined for condition A and B, respectively: Complex I - 0.20 and 0.64, Complex III - 0.41 and 0.40, Complex IV - 0.40 and 0.49, ANT - 0.20 and 0.92, ATP synthase - 0.065 and 0.38, Pi carrier - 0.06 and 0.06, MtCK 0.95. The sum of C(vi)(JATP) was 1.33 and 3.84, respectively. Thus, C(vi)(JATP) were specifically increased under conditions B only for steps involved in ADP turnover and for Complex I in permeabilized cardiomyocytes within Mitochondrial Interactosome, a supercomplex consisting of MtCK, ATP-Synthasome, voltage dependent anion channel associated with tubulin ßII which restricts permeability of the mitochondrial outer membrane.

Membrane transport of fatty acylcarnitine and free L-carnitine by rat liver microsomes.

Recent studies have suggested that parts of the hepatic activities of diacylglycerol acyltransferase and acyl cholesterol acyltransferase are expressed in the lumen of the endoplasmic reticulum (ER). However the ER membrane is impermeable to the long-chain fatty acyl-CoA substrates of these enzymes. Liver microsomal vesicles that were shown to be at least 95% impermeable to palmitoyl-CoA were used to demonstrate the membrane transport of palmitoylcarnitine and free L-carnitine - processes that are necessary for an indirect route of provision of ER luminal fatty acyl-CoA through a luminal carnitine acyltransferase (CAT). Experimental conditions and precautions were established to permit measurement of the transport of [14C]palmitoylcarnitine into microsomes through the use of the luminal CAT and acyl-CoA:ethanol acyltransferase as a reporter system to detect formation of luminal [14C]palmitoyl-CoA. Rapid, unidirectional transport of free L-[3H]carnitine by microsomes was measured directly. This process, mediated either by a channel or a carrier, was inhibited by mersalyl but not by N-ethylmaleimide or sulfobetaine - properties that differentiate it from the mitochondrial inner membrane carnitine/acylcarnitine exchange carrier. These findings are relevant to the understanding of processes for the reassembly of triacylglycerols that lipidate very low density lipoprotein particles as part of a hepatic triacylglycerol lipolysis/re-esterification cycle.

N-ethylmaleimide and mercurials modulate inhibition of the mitochondrial inner membrane anion channel by H+, Mg2+ and cationic amphiphiles.

Previously it has been shown that the mitochondrial inner membrane anion channel is reversibly inhibited by matrix Mg2+, matrix H+ and cationic amphiphiles such as propranolol. Furthermore, the IC50 values for both Mg2+ and cationic amphiphiles are dependent on matrix pH. It is now shown that pretreatment of mitochondria with N-ethylmaleimide, mersalyl and p-chloromercuribenzenesulfonate increases the IC50 values of these inhibitors. The effect of the mercurials is most evident when cysteine or thioglycolate is added to the assay medium to reverse their previously reported inhibitory effect (Beavis, A.D. (1989) Eur. J. Biochem. 185, 511-519). Although the IC50 values for Mg2+ and propranolol are shifted they remain pH dependent. Mersalyl is shown to inhibit transport even in N-ethylmaleimide-treated mitochondria indicating that N-ethylmaleimide does not react at the inhibitory mercurial site. However, the effects of N-ethylmaleimide and mersalyl on the IC50 for H+ are not additive which suggests that mercurials and N-ethylmaleimide react at the same 'regulatory' site. It is suggested that modification of this latter site exerts an effect on the binding of Mg2+, H+ and propranolol by inducing a conformational change. It is also suggested that a physiological regulator may exist which has a similar effect in vivo.

The mitochondrial inner-membrane anion channel possesses two mercurial-reactive regulatory sites.

The mitochondrial inner membrane anion channel catalyzes the electrophoretic transport of a wide variety of anions and is inhibited by matrix divalent cations and protons. In this paper, evidence is provided that mersalyl and p-chloromercuribenzene-sulfonate each interact with this uniporter at two distinct sites. Binding to site 1 causes a shift in the pH dependence of transport, characterized by a decrease in the pIC50 for protons from about 7.8 to about 7.3, and leads to substantial stimulation of transport in the physiological pH range. This effect is not reversed by addition of thiols such as thioglycolate. Binding of mersalyl and p-chloromercuribenzenesulfonate to site 2 inhibits the transport of most anions including Pi, citrate, malonate, sulfate and ferrocyanide. The transport of Cl- is inhibited about 60% by mersalyl, but is not inhibited by p-chloromercuribenzenesulfonate. These data suggest that inhibition is a steric effect dependent on the size of the anion and the size of the R group of the mercurial. This inhibition is reversed by thioglycolate. Dose/response curves indicate that mersalyl binds to site 1 as the dose increased from 7 to 13 nmol/mg, whereas it binds to site 2 as the dose is increased from 10 to 18 nmol/mg. Thus, at certain pH values both stimulatory and inhibitory phases can be seen in the same dose/response curve. It is suggested that these sites may contain thiol groups and that physiological regulators may exist which can effect changes in activity of the inner membrane anion uniporter similar to those exerted by mercurials.

Fumarate permeation in rat liver mitochondria: fumarate/malate and fumarate/phosphate translocators.

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.

Androgen receptor in the rabbit liver and apparent translocation to the nucleus in vivo.

The present study demonstrates that the liver of a mammal, the rabbit, contains an androgen receptor. Rabbit liver cytosol or purified nuclei were incubated with the radioactive androgen R-1881 (methyltrienolone). The cytosol of adult female rabbit liver contained androgen-binding sites of high affinity, Kd 0.9 nM, and a capacity of 7000 fmol/g liver or 79 fmol/mg cytosol protein. After partial purification by 35% ammonium sulfate precipitation (AS cytosol), the binding specificity pattern was consistent with that of androgen receptor. Apparent translocation from cytosol to nucleus was examined by administering 100 micrograms nonradioactive R-1881 in vivo. One hour later, almost all of the receptor was detected in liver nuclei. The receptor concentration in purified nuclei, as determined by an exchange procedure, was 2100 fmol/g liver, which is an increase of 6-fold relative to the low levels in nuclei of untreated rabbits. The binding affinity, specificity pattern, and protease sensitivity for the sites in the nucleus after in vivo androgen in general resembled those as AS cytosol binding in untreated liver. Androgen receptors were also present in AS cytosol of the immature female rabbit liver and, in lower concentration, of the intact adult male rabbit. The properties of liver androgen binding are quite different from those of testosterone binding protein present in serum. Accordingly, an androgen binding protein with high affinity and specificity and capable of translocation to the nucleus in vivo has been detected in mammalian liver. An androgen receptor in the mammalian liver may mediate androgen effects on liver function, including modulation of synthesis of selective plasma proteins.

Reaction of mersalyl with mitochondrial proteins under native and denaturing conditions as exemplified by the identification and isolation of the phosphate carrier.

Pig heart mitochondria were incubated with [203Hg]mersalyl and the radioactive pattern was analyzed by fluorography after dodecyl sulfate gel electrophoresis. No differences in the radioactivity distribution were found after labeling with various mersalyl concentrations, at different pH and after labeling in the native or dodecyl sulfate-dissociated state of mitochondria. A redistribution of [203Hg]mersalyl between various proteins in the presence of dodecyl sulfate could directly be demonstrated by mixing labeled membranes with unlabeled matrix proteins, as well as by comparison of the radioactivity patterns of whole mitochondria labeled with irreversibly reacting N-([2-3H]ethyl)maleimide and reversibly binding [203Hg]mersalyl. From these data it is concluded that under native conditions mersalyl is principally bound to the phosphate carrier protein, whereas during dissociation in dodecyl sulfate the organomercurial is redistributed and mainly attached to the ADP/ATP-carrier protein.

Autoradiographic changes in the kidney of the whole-body sublethally x-ray irradiated rat.

203Hg-hydroxymersalyl uptake / gram of kidney (HU), renal autoradiographic and histologic aspect after 800 R X-ray whole-body rat irradiation was studied. Twenty-four to seventy-two hours after irradiation, HU increased, while tubular autoradiographic granularity decreased. Their return to the control levels occurred gradually within two weeks. The relations of these findings to the early circulatory and dystrophic changes, as well as to the subsequent postirradiation restoring renal process are discussed.

Mechanism of inhibition of the dicarboxylate carrier of mitochondria by thiol reagents.

The nature of the inhibition of the dicarboxylate carrier by compounds reacting with SH groups has been investigated. (1) Mersalyl and p-hydroxymercuribenzoate increase the Km without changing the V of malonate/Pi exchange, when they are added simultaneously with the dicarboxylate. If, on the other hand, the mitochondria are preincubated with SH reagents prior to the addition of malonate, the mersalyl inhibition of malonate/Pi exchange becomes predominantly non-competitive with respect to malonate. (2) In the case of Pi/Pi exchange, catalyzed by the dicarboxylate carrier, the mersalyl inhibition is competitive with respect to Pi (as indicated by Lineweaver-Burk plots), even when mersalyl is added before the substrate. Dixon plots of the rate of Pi uptake against mersalyl concentration are, however, non-linear, suggesting that the inhibition is partially competitive. (3) Dicarboxylates and dicarboxylate analogous protect against SH reagent inhibition of both dicarboxylate and Pi uptake via the dicarboxylate carrier. The protectors are effective when added before, or together with the SH reagents, but do not reverse the inhibition once it has been established. Protection by substrate analogues progressively decreases, as the time of incubation with the SH reagent increases. (4) The presence of Pi does not protect against the SH reagent inhibition of the Pi uptake. (5) The rate of SH reagent inhibition of the dicarboxylate carrier is competively inhibited by dicarboxylates. (6) It is concluded that SH reagents bind at or near the dicarboxylate specific binding site and distant from the Pi binding site. As a result of this reaction these inhibitors prevent dicarboxylate binding directly and decrease the affinity for Pi by an indirect conformational change.