The role of sulfhydryl groups in oxidative phosphorylation and ion transport by rat liver mitochrondia

The Role of the Thioredoxin System in Brain Diseases

The thioredoxin system, consisting of thioredoxin (Trx), thioredoxin reductase (TrxR), and NADPH, plays a fundamental role in the control of antioxidant defenses, cell proliferation, redox states, and apoptosis. Aberrations in the Trx system may lead to increased oxidative stress toxicity and neurodegenerative processes. This study reviews the role of the Trx system in the pathophysiology and treatment of Alzheimer's, Parkinson's and Huntington's diseases, brain stroke, and multiple sclerosis. Trx system plays an important role in the pathophysiology of those disorders via multiple interactions through oxidative stress, apoptotic, neuro-immune, and pro-survival pathways. Multiple aberrations in Trx and TrxR systems related to other redox systems and their multiple reciprocal relationships with the neurodegenerative, neuro-inflammatory, and neuro-oxidative pathways are here analyzed. Genetic and environmental factors (nutrition, metals, and toxins) may impact the function of the Trx system, thereby contributing to neuropsychiatric disease. Aberrations in the Trx and TrxR systems could be a promising drug target to prevent and treat neurodegenerative, neuro-inflammatory, neuro-oxidative stress processes, and related brain disorders.

The Effect of N-Acetylcysteine on Respiratory Enzymes, ADP/ATP Ratio, Glutathione Metabolism, and Nitrosative Stress in the Salivary Gland Mitochondria of Insulin Resistant Rats

This is the first study to assess the effect of N-acetylcysteine (NAC) on the mitochondrial respiratory system, as well as free radical production, glutathione metabolism, nitrosative stress, and apoptosis in the salivary gland mitochondria of rats with high-fat diet (HFD)-induced insulin resistance (IR). The study was conducted on male Wistar rats divided into four groups of 10 animals each: C (control, rats fed a standard diet containing 10.3% fat), C + NAC (rats fed a standard diet, receiving NAC intragastrically), HFD (rats fed a high-fat diet containing 59.8% fat), and HFD + NAC (rats fed HFD diet, receiving NAC intragastrically). We confirmed that 8 weeks of HFD induces systemic IR as well as disturbances in mitochondrial complexes of the parotid and submandibular glands of rats. NAC supplementation leads to a significant increase in the activity of complex I, II + III and cytochrome c oxidase (COX), and also reduces the ADP/ATP ratio compared to HFD rats. Furthermore, NAC reduces the hydrogen peroxide production/activity of pro-oxidant enzymes, increases the pool of mitochondrial glutathione, and prevents cytokine formation, apoptosis, and nitrosative damage to the mitochondria in both aforementioned salivary glands of HFD rats. To sum up, NAC supplementation enhances energy metabolism in the salivary glands of IR rats, and prevents inflammation, apoptosis, and nitrosative stress.

The ADP and ATP transport in mitochondria and its carrier

Different from some more specialised short reviews, here a general although not encyclopaedic survey of the function, metabolic role, structure and mechanism of the ADP/ATP transport in mitochondria is presented. The obvious need for an "old fashioned" review comes from the gateway role in metabolism of the ATP transfer to the cytosol from mitochondria. Amidst the labours, 40 or more years ago, of unravelling the role of mitochondrial compartments and of the two membranes, the sequence of steps of how ATP arrives in the cytosol became a major issue. When the dust settled, a picture emerged where ATP is exported across the inner membrane in a 1:1 exchange against ADP and where the selection of ATP versus ADP is controlled by the high membrane potential at the inner membrane, thus uplifting the free energy of ATP in the cytosol over the mitochondrial matrix. Thus the disparate energy and redox states of the two major compartments are bridged by two membrane potential responsive carriers to enable their symbiosis in the eukaryotic cell. The advance to the molecular level by studying the binding of nucleotides and inhibitors was facilitated by the high level of carrier (AAC) binding sites in the mitochondrial membrane. A striking flexibility of nucleotide binding uncovered the reorientation of carrier sites between outer and inner face, assisted by the side specific high affinity inhibitors. The evidence of a single carrier site versus separate sites for substrate and inhibitors was expounded. In an ideal setting principles of transport catalysis were elucidated. The isolation of intact AAC as a first for any transporter enabled the reconstitution of transport for unravelling, independently of mitochondrial complications, the factors controlling the ADP/ATP exchange. Electrical currents measured with the reconstituted AAC demonstrated electrogenic translocation and charge shift of reorienting carrier sites. Aberrant or vital para-functions of AAC in basal uncoupling and in the mitochondrial pore transition were demonstrated in mitochondria and by patch clamp with reconstituted AAC. The first amino acid sequence of AAC and of any eukaryotic carrier furnished a 6-transmembrane helix folding model, and was the basis for mapping the structure by access studies with various probes, and for demonstrating the strong conformation changes demanded by the reorientation mechanism. Mutations served to elucidate the function of residues, including the particular sensitivity of ATP versus ADP transport to deletion of critical positive charge in AAC. After resisting for decades, at last the atomic crystal structure of the stabilised CAT-AAC complex emerged supporting the predicted principle fold of the AAC but showing unexpected features relevant to mechanism. Being a snapshot of an extreme abortive "c-state" the actual mechanism still remains a conjecture.

S-allylcysteine inhibits free radical production, lipid peroxidation and neuronal damage in rat brain ischemia

The efficacy of S-allylcysteine (SAC) as a free radical scavenger was studied using rat brain ischemia models. In a middle cerebral artery occlusion model, preischemic administration of SAC had the following effects: it improved motor performance and memory impairment and reduced water content and the infarct size. In a transient global ischemia model, the time course of free radical (alkoxyl radical) formation as studied by electron paramagnetic resonance (EPR) spectroscopy and alpha-phenyl-N-tert-butylnitrone (PBN) was biphasic; the first peak occurred at 5 min and the second at 20 min after reperfusion. Although SAC did not attenuate the first peak, it did affect the second peak, which is related to lipid peroxidation. The lipid peroxidation as estimated by thiobarbituric acid reactive substances (TBARS) increased significantly at 20 min after reperfusion. SAC decreased TBARS to the levels found without ischemia. These results suggest that SAC could have beneficial effects in brain ischemia and that the major protective mechanism may be the inhibition of free radical-mediated lipid peroxidation.

Regulation of the activity of choline acetyl transferase by lipoic acid

The observations reported in this article demonstrate that lipoic acid strongly influences the activity of a purified preparation of choline acetyl transferase. The reduced form, dihydrolipoic acid, is a powerful activator of the enzyme while lipoic acid itself has an inhibitory effect and counteracts the stimulatory effect of dihydrolipoic acid. It is proposed that dihydrolipoic acid serves an essential function in the action of this enzyme and that the ratio of reduced to oxidized lipoic acid in the cell may play an important role in the regulation of the activity of the enzyme. The implications of these findings for cell function and acetyl choline formation are discussed.

Reflections on the role of the thiol group in biology

This essay is concerned with the role of the thiol or sulfhydrvl group in cellular function and metabolism and with the important investigations over many years that have led us to a better understanding of the importance of this molecular moiety that plays such a vital role in biology. The tools for measuring the SH group and for inhibiting or regenerating it will be discussed as will its essential role in the actions of many enzymes. The importance of the thiol group in glycolysis and in energy production by mitochondria will be emphasized. Of special interest at present is the fact that certain low molecular weight SH-containing substances can mimic some of the actions of insulin and may become of benefit in the treatment of diabetes mellitus. Finally, the toxic effects of oxygen on metabolism and function will be discussed with particular reference to the possibility that oxidation of thiol groups may play a role in the manifestations of oxygen toxicity.

4-Hydroxy-2(E)-nonenal inhibits CNS mitochondrial respiration at multiple sites

A destructive cycle of oxidative stress and mitochondrial dysfunction is proposed in neurodegenerative disease. Lipid peroxidation, one outcome of oxidative challenge, can lead to the formation of 4-hydroxy-2(E)-nonenal (HNE), a lipophilic alkenal that forms stable adducts on mitochondrial proteins. In this study, we characterized the effects of HNE on brain mitochondrial respiration. We used whole rat brain mitochondria and concentrations of HNE comparable to those measured in patients with Alzheimer's disease. Our results showed that HNE inhibited respiration at multiple sites. Complex I-linked and complex II-linked state 3 respirations were inhibited by HNE with IC50 values of approximately 200 microM HNE. Respiration was apparently diminished owing to the inhibition of complex III activity. In addition, complex II activity was reduced slightly. The lipophilicity and adduction characteristics of HNE were responsible for the effects of HNE on respiration. The inhibition of respiration was not prevented by N-acetylcysteine or aminoguanidine. Studies using mitochondria isolated from porcine cerebral cortex also demonstrated an inhibition of complex I- and complex II-linked respiration. Thus, in neurodegenerative disease, oxidative stress may impair mitochondrial respiration through the production of HNE.

Kinetic analysis of 75selenium uptake by mitochondria of germinating Vigna radiata of different selenium status

Earlier studies in our laboratory demonstrated the beneficial role of Se in Vigna radiata, a Se-deficient legume, during germination, as reflected in growth-related parameters and specific uptake of 75Se. Uptake of Na2(75)SeO3, added in vitro by mitochondria isolated from seedlings germinated in control (without Se), and Se-supplemented groups (0.5, 1.0, and 2.0 ppm Se) indicated a proportional increase in the uptake with added Na2(75)SeO3, in concentrations up to 25 microM. The uptake of 75Se, increased linearly with time up to 15 min and a definite efflux followed at 30 min. The results were indicative of cooperative effects during Se transport. Kinetic analyses of the uptake of 75Se during time intervals of 15 and 30 min were carried out both in the whole mitochondria and the mitochondrial protein fractions. Graphical analyses using Lineweaver-Burk plot, Hill plot, log [v] vs log [A] and Scatchard plot confirmed the existence of negative cooperativity during 75Se uptake. Hill coefficient (nH) values were estimated to be around 0.7-0.8. Scatchard plots for 75Se uptake were biphasic, suggesting the probable presence of two classes of binding sites. The number of high and low affinity binding sites were estimated to be around 4-7 and 26-30 nmol/mg protein, respectively. Studies with mitochondrial respiratory inhibitors indicated about 10-20% of the total 75Se uptake to be energy dependent. Inhibition of 75Se uptake by about 60-70% by sulfate and sulfite (5-25 microM) implies the involvement of dicarboxylate port in Se transport. A decrease in the uptake of 75Se by 40-60% effected by CdCl2, HgCl2, mersalyl, and NEM confirmed the interaction of thiols in the process. Evidence for the regulatory nature of 75Se uptake by mitochondria of V. radiata emerges from the present study.

N-acetylcysteine protects against age-related decline of oxidative phosphorylation in liver mitochondria

Since it has been proposed that oxygen radical inactivation of key enzymes plays a critical role in cell aging, we have investigated the effects of a thiolic free radical scavenger on the oxidative phosphorylation enzymes of liver mitochondria from female OF-1 mice. At 48 weeks of age a control group was fed standard food pellets and another group received pellets containing 0.3% (w/w) of N-acetylcysteine. A 24-week treatment resulted in a significant increase in the specific activities of complex I, IV and V in the hepatic mitochondria of the N-acetylcysteine-treated animals as compared to aged controls.

Aging and protein oxidative damage

The hypothesis that aging is associated with the accumulation of oxidative damage was tested in the adult male housefly by monitoring the loss of membrane protein -SH groups, and activities of glucose-6-phosphate dehydrogenase and alcohol dehydrogenase, the cytosolic enzymes that are particularly susceptible to oxidative damage. Membrane protein -SH content and activities of these enzymes decreased with age and were correlated with the life expectancy or physiological age rather than the chronological age of the flies. Because the experimentally-induced loss of membrane protein -SH groups has a demonstrable deleterious effect on a variety of cellular functions, such damage during aging can be hypothesized to contribute to the physiological attrition associated with senescence.

Selenium-mediated biochemical changes in Japanese quails : Tissue uptake and distribution of injected(75)selenium labeled sodium selenite in relation to dietary selenium status

The tissue uptake and distribution of injected [(75)Se]-sodium selenite as a variance with time and as influenced by dietary selenium status was followed in the tissues of Japanese quails,Coturnix coturnix japonica. Quails maintained on a low selenium semipurified (basal) diet and basal diets supplemented with 0.2 and 2.0 ppm selenium as sodium selenite were injected intraperitonially with(75)Se as sodium selenite (2.8 microcuries). The injected(75)Se was monitored in blood, liver, kidney, heart, and testis at 24, 72, and 144 h after injection. Maximal uptake of the injected(75)Se was observed in tissues of quails maintained on basal diet. The uptake of(75)Se in tissues in general was determined by the dietary Se status. Among the organs studied, kidney had the maximal level of(75)Se, 0.2 ppm (μg/g wet tissue) followed by liver, testis, and heart, but testis had the maximal level when the level per milligram of protein was considered, about 3.0 ng/mg protein, followed by liver, kidney, and heart. About 10-20% of the tissue(75)Se was located in the mitochondria and 50-60% in the post-mitochondrial supernatant fractions in all dietary Se levels. Significant incorporation of(75)Se in the mitochondrial membrane was observed. The percent distribution ratio between the membrane and matrix fractions of the mitochondria remained constant at all dietary Se levels which, in liver was 65∶35, in kidney 55∶45, and in testis 75∶25. However, in heart mitochondria, the distribution of(75)Se between membrane and matrix varied with dietary Se status, the ratio being 82∶18 in the basal group, and 72∶28 and 41∶59 in the 0.2 and 2.0 ppm Se-supplemented groups, respectively. This is indicative of a preferential uptake of(75)Se in the mitochondrial membrane in conditions of deficiency. About 40-60% of the mitochondrial membrane-associated(75)Se was released upon Triton treatment in all the organs. Of the membrane-bound(75)Se, about 10-15% was acid-labile in liver and kidney and 25% in the heart tissue. Possibilities of tissue specific roles, especially in the heart mitochondrial membrane-related processes, are indicated for selenium.

Thiazolidine-4-carboxylic acid, a physiologic sulfhydryl antioxidant with potential value in geriatric medicine

Thiazolidine-4-carboxylic acid (TC) is a cyclic sulfur amino acid, a condensation product of cysteine and formaldehyde. The chemistry, biological effects and clinical use of TC are reviewed. Extensive animal experiments and studies on human subjects carried out in Europe indicate that a combination of TC and folic acid, 'Folcysteine', has revitalizing effects on age-related biochemical variables of blood and tissues. Further animal studies confirmed the anti-toxic effects of TC, particularly on the liver. The evidence accumulated so far suggests that addition of TC to the diet slows the aging process in mammals and prolongs their life span. On the other hand, findings suggesting that TC caused reverse transformation of tumor cells into normal cells and was effective against human cancers could not be confirmed in additional studies. TC has been clinically used for about 20 yr, mainly in the treatment of liver diseases and related gastrointestinal disturbances. Derivatives of TC with similar applications have been developed. Djenkolic acid is a naturally occurring relative of TC which is abundant in djenkol beans. The toxic effects of djenkolic acid and its possible conversion into TC are discussed.

Effect of alloxan on the transport of dicarboxylate, tricarboxylate, pyruvate and glutamate in isolated mouse liver mitochondria

The effect of alloxan on anion transport in isolated mouse liver mitochondria was studied with the swelling technique. Mitochondria pre-incubated with alloxan exhibited partial inhibition of the transport of malate, citrate, pyruvate and glutamate. 2n-butylmalonate caused complete inhibition of malate transport, and the translocation of citrate was completely blocked by 1,2,3-benzenetricarboxylate, while N-ethylmaleimide inhibited glutamate transport partially. The observation that alloxan inhibits different mitochondrial anion transport mechanisms emphasizes that the drug profoundly affects mitochondrial function.

The interaction of cadmium and certain other metal ions with proteins and nucleic acids

The toxic effects of cadmium and other selected divalent cations are presumed to be related to specific chemical and physical characteristics of the ion. The chemistry of cadmium and metal ions in general is reviewed from the viewpoint of such relevant properties as ion polarizability, electronic structure, and the hard-soft characteristics. The softness of metal ions is seen as a useful single parameter to correlate with the affinity for nucleic acids and proteins and with toxic effects. The effects of cadmium on nucleic acids and proteins are examined for a number of specific cases to illustrate the variety of interactions that are well recognized and to demonstrate the utility of soft metal ions as reagents and probes for examining the relationship of structure and function in these macromolecules.

Influence of the energetic state of mitochondria on the inhibition of oxidative phosphorylation by N-ethylmaleimide

N-Ethylmaleimide inhibitory effect on oxidative phosphorylation, adenylic nucleotide translocation, succinate dehydrogenase and succinoxidase activities was studied as a function of the energetic state of mitochondria. 1. Using a reversible thiol reagent (mersalyl), in order to protect the phosphate carrier against irreversible action of N-ethylmaleimide, it was found that: (a) when mersalyl-pretreated mitochondria were in a 'non-energized' state, i.e. preincubated without a substrate and in the presence of rotenone, only a slight inhibition of succinate oxidation coupled to ATP synthesis by N-ethylmaleimide was observed. (b) when mersalyl-pretreated mitochondria were in an 'energized' state, i.e. preincubated in the presence of an oxidizable substrate, N-ethylmaleimide strongly inhibited the coupled oxidation of succinate. 2. Mitochondrial energization was also shown to enhavce the inhibitory effect of N-ethylmaleimide on adenylic nucleotide translocation and succinoxidase activity. However, other sulphydrul groups seem to be involved in the inhibition mechanism, but their function is unknown. 3. As N-ethylmaleimide inhibitory effect increased, an enhancement of N-[14C]ethylmaleimide binding to mitochondrial sulphydryl groups was obtained.

Ca2+ transport by chondrocyte mitochondria of the epiphyseal growth plate

In a study of the Ca2+ kinetics of mitochondria of chick epiphyseal chondrocytes, the rate of Ca2+ uptake was linear up to a medium Ca2+ concentration of 30 mum. The half maximal transport rate occurred at 34 mum Ca2+. The Ca2+ uptake rate, expressed as a function of time, was 35 nmoles/mg protein/min; the presence of Mg2+ had little effect on Ca2+ accumulation. While these kinetic parameters did not differ significantly from mitochondria of cells of nonmineralizing tissues, the respiratory characteristics of the chondrocyte organelles exhibited functional differences. Thus, up to 350 nmoles Ca2+/mg protein, chondrocyte mitochondria performed coupled oxidative phosphorylation. Calcium uptake was energy supported, while Ca2+ binding was low. Addition of respiratory inhibitors and uncouplers to these mitochondria resulted in a rapid loss of more than 80% of the total Ca2+. The Ca/Pi ratio of the extrudate was very similar to the ratio of the ions in cartilage septum fluid. In the most mineralized zones of the epiphyseal plate, there was little change in the state 4 respiratory rate, but nonspecific Ca2+ binding was elevated and a high percentage of the total Ca2+ was in a nonextrudable form. The results indicate that in cells preparing for mineralization, much of the total mitochondrial Ca2+ is in a form that can be transported to the calcification front. In cells close to the calcification front, nonextrudable Ca2+ may form calcium phosphate granules described by other investigators.

Influence of the energetic state of rat liver mitochondria on the sensitivity of the phosphate carrier towards SH reagents

Phosphate transport into rat liver mitochondria was measured by the swelling technique in 0.1 M ammonium phosphate. Energized or non-energized mitochondria were preincubated with different thiol reagents and evidence is given that with a slow-reacting thiol reagent, ethacrynate, the inactivation of the phosphate carrier is obtained when mitochondria are energized, while poor or no inactivation occurs when mitochondria are non-energized or preincubated with Pi. Moreover, the inactivation depends on the presence of Mg2+ and on the nature of the substrate. Some comparative essays were done using N-ethylmaleimide as a thiol reagent, but no energy-linked variation of N-ethylmaleimide inhibition on phosphate transport was obtained. Taking into account the fact that both thiol-reagents incorporation into rat liver mitochondria is sitmulated by the presence of substrate, the different behaviour of these two thiol-reagents towards Pi transport is discussed on the basis of their different reactivity with SH groups.

Heterogeneity of chondrocyte mitochondria. A study of the Ca2+ concentration and density banding characteristics of normal and rachitic cartilage

Previous morphological studies of the mineralizing epiphysis suggested that some mitochondria were concerned with Ca2+ accumulation while others were associated with cellular energetics and metabolism. To determine if there was mitochondrial heterogeneity in chondrocytes of the epiphyseal growth plate, mitochondria were isolated from four different regions of the plate and subjected to continuous sucrose gradient centrifugation. Centrifugation of the organelles in a narrow density sucrose gradient (1.5--2.0 M) in the presence of inhibitors of Ca2+ transport (ruthenium red and 5,5'-dithiobis-(2-nitrobenzoic acid)) revealed that considerable heterogeneity existed. In the least calcified zone 20% of the mitochondria formed a low density band of low Ca2+ concentration (309 nmol/mg protein). Organelles isolated from more calcified tissue zones showed a concomitant increase in Ca2+ concentration (up to 5700 nmol/mg protein) as well as an increase in the total percentage of mitochondria sedimenting in 2.0 M sucrose. The banding patterns of mitochondria isolated from rachitic and hypertrophic cartilage were similar. In addition, similarities were also noted in the Ca2+ concentration and the cytochrome oxidase activities of mitochondria of these tissues. During recovery from the rachitic condition, there was a change in the density centrifugation characteristics of this tissue and a substantial increase was noted in the proportion of mitochondria sedimenting in 2.0 M sucrose. The Ca2+ concentration of mitochondria of this rapidly calcifying tissue suggested that the critical Ca2+ concentration necessary for initiation of the calcification mechanism was 4 mumol/mg protein.

Reactions of bis(thiosemicarbazonato) copper(II) complexes with tumor cells and mitochondria

The respiration of Ehrlich ascites tumor cells is inhibited by 3-ethoxy-2-oxobutyraldehyde bis (thiosemicarbazanato) copper (II). State 3 oxidative phosphorylation in mitochondria from tumor cells is also inhibited, with the effect more pronounced using glutamate or pyruvate-malate as substrates than with succinate. The disruption of oxidative phosphorylation in bovine heart mitochondria is qualitatively similar. The principal site of inhibition is in coupling site one, energetically between the electron transport site chain and the locus of uncoupling by 2,4-dinitrophenol. This appears to contain thiol groups which are oxidized by the complex. For a series of bis (thiosemicarbazonato) copper complexes, the extent of inhibition of heart mitochondrial oxidative phosphorylation is correlated with the reduction potentials of the complexes and with their in vitro cytotoxic effects against Walker 256 carcinoma tumor cells.

Special features of Pi transport in pig heart and rat liver mitochondria as revealed by 6,6'-dithiodinicotinic acid (CPDS)

CPDS (6,6'-dithiodinicotinic acid), a non permeant thiol agent which affects several mitochondrial functions in a way different to that of mersalyl [18-19] revealed striking differences between the phosphate translocating systems of pig heart and rat liver mitochondria. Pi entry was measured either by swelling in 0.12 M ammonium phosphate or by rapid centrifugation in 32Pi medium. Pi efflux was measured after preloading of mitochondria with 32Pi, by exchange against Pi or malate; the "ATP-FCCP" system has been tested previously [19]. In pig heart mitochondria, Pi entry seems to proceed exclusively via the Pi/OH- carrier; CPDS completely inhibits this transport and the energy-linked functions. In contrast n-butyl-malonate does not affect the Pi-entry and the energy-linked functions. The Pi efflux is not affected either by CPDS or mersalyl, which do not produce a swelling in the "ATP-uncoupler system". In rat liver mitochondria, CPDS inhibits only the Pi/OH- carrier; both CPDS and n-butylmalonate are necessary to inhibit completely Pi entry. CPDS as well as mersalyl provokes a swelling in the presence of the "APT-uncoupler system". The results suggest two distinct functions of phosphate transport in both types of mitochondria.

A kinetic study of mitochondrial calcium transport

This report describes a kinetic analysis of energy-linked Ca2+ transport in rat liver mitochondria, in which a ruthenium red/EGTA [ethanedioxy-bis(ethylamine)-tetraacetic acid] quenching technique has been used to measure rates of 45Ca2+ transport. Accurately known concentrations of free 45Ca2+ were generated with Ca2+/nitrilotriacetic acids buffers for the determination of substrate/velocity relationships. The results show that the initial velocity of transport is a sigmoidal function of Ca2+ concentration (Hill coefficient = 1.7), the Km being 4 muM Ca4 at 0 degrees C and pH 7.4. These values for the Hill coefficient and the Km remain constant in the presence of up to 2 mM phosphate, but with 10 mM acetate both parameters are increased slightly. Both permeant acids increase the maximum velocity to an extent dependent on their concentration. The Ca2+-binding site(s) of the carrier contains a group ionizing at pH approximately 7.5 at 0 degrees C, which is functional in the dissociated state. The stimulatory effect of permeant acids is ascribed to their facilitating the release of Ca2+ from the carrier to the internal phase, an interpretation which is strengthened by the lack of effect of the permeant anion SCN- on Ca2+ transport. Studies on the time-course of Ca2+ uptake and of EFTA-induced Ca2+ efflux from pre-loaded mitochondria demonstrate the reversibility of the carrier in respiring mitochondria and the extent to which this property is influenced by permeant acids. These data are accommodated in a carrier mechanism based on electrophoretic transport of Ca2+ bound to pairs of interacting acidic sites.

Ozone interaction with rodent lung. III. Oxidation of reduced glutathione and formation of mixed disulfides between protein and nonprotein sulfhydryls

Nonprotein sulfhydryls (NPSH), a major source of cellular reducing substances, were examined in lung tissue after short-term exposure of rats to O3. While the NPSH level was unaffected by low-level exposures (e.g., 0.8 ppm for up to 24 h or 1.5 ppm for up to 8 h), it was significantly lowered by higher exposure regimens (e.g., 25 per cent after 2 ppm for 8 h and 49 per cent after 4 ppm for 6 h). After exposure to 4 ppm O3 for 6 h the level of reduced glutathione (GSH), which accounted for approximately 90 per cent of NPSH in the lung, decreased 40 per cent but without a rise in the level of oxidized gluathione (GSSG). Treatment of lung homogenate with borohydride led to recovery of NPSH in exposed lungs to control values, suggesting that NPSH or GSH oxidation during in vivo O3 exposure resulted in formation of mixed disulfides with other sulfhydryl (SH) groups of lung tissue. Extracts of borohydride-treated particulate and supernatant fractions of lung homogenate were analyzed for NPSH by paper chromatography. From this analysis GSH appeared to be the only NPSH bound to lung tissue proteins via mixed disulfide linkage. The formation of mixed disulfides appeared to be a transient phenomenon. Immediately after a 4-h exposure to 3 ppm O3 the level of mixed disulfides was small (15 per cent of the total NPSH) but attained a peak (equivalent to 0.6 mumol NPSH/lung) after a recovery for 24 h. However, the level diminished considerably within 48 h of recovery.