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PubMed1981

Phosphate transport in rat liver mitochondria: location of sulfhydryl groups essential for transport activities.

The membrane orientation and symmetry of protein thiol group(s) necessary for transport of Pi in rat liver mitochondria have been assessed by comparing inhibition of transport in intact mitochondria to that in inverted vesicles of purified inner membrane. The permeability characteristics of a variety of inhibitors have been determined under specified conditions. The sensitivities of the uptake pathways in mitochondria and in inverted vesicles appear thus far to be identical. By comparing results with permeant and nonpermeant inhibitors, or sequential treatment with different inhibitors, arguments can be made in favor of a single reorienting site of thiol sensitivity.

Animals↗
PubMed1993

Purification and characterization of catalase from goat (Capra capra) lung.

Catalase plays a major role in the protection of tissues from toxic effects of H2O2 and partially reduced oxygen species. In the present study catalase was extracted and purified 330-fold from goat lung by acetone fractionation and successive chromatographies on DEAE-cellulose, Sephadex G-200, Blue Sepharose CL-6B and Ultrogel AcA-34. The purified enzyme was almost homogeneous as judged by polyacrylamide gel electrophoresis and FPLC. The molecular weight and Stokes' radius of the purified enzyme were 339 kDa and 127 +/- 2 A. The enzyme had 11 sulfhydryl groups and 15 tryptophan groups per mol of the enzyme. A broad pH optimum in the range 5.2 to 7.8 was obtained. Sulfhydryl group binding agents, thiol reagents and N-Bromosuccinimide inhibited the enzyme activity. The kinetic data show no cooperativity between the substrate binding sites. Tryptophan, indole acetic acid, cysteine, formaldehyde and sodium azide inhibited the enzyme non-competitively with Ki values of 1.5, 1.6, 6.7, 0.55 and 0.0017 mM, respectively.

Amino Acids↗
PubMed1993

Roles of sulfhydryl and disulfide groups in the binding of CP-55,940 to rat brain cannabinoid receptor.

The roles of sulfhydryl and disulfide groups in the specific binding of synthetic cannabinoid CP-55,940 to the cannabinoid receptor in membrane preparations from the rat cerebral cortex have been examined. Various sulfhydryl blocking reagents including p-chloromercuribenzoic acid (p-CMB), N-ethylmaleimide (NEM), o-iodosobenzoic acid (o-ISB), and methyl methanethiosulfonate (MMTS) inhibited the specific binding of [3H]CP-55,940 to the cannabinoid receptor in a dose-dependent manner. About 80-95% inhibition was obtained at a 0.1 mM concentration of these reagents. Scatchard analysis of saturation experiments indicates that most of these sulfhydryl modifying reagents reduce both the binding affinity (Kd) and capacity (Bmax). On the other hand, DL-dithiothreitol (DTT), a disulfide reducing agent, also irreversibly inhibited the specific binding of [3H]CP-55,940 to the receptor and about 50% inhibition was obtained at a 5 mM concentration. Furthermore, 5 mM DTT was abelt to dissociate 50% of the bound ligand from the ligand-receptor complex. The marked inhibition of [3H]CP-55,940 binding by sulfhydryl reagents suggests that at least one free sulfhydryl group is essential to the binding of the ligand to the receptor. In addition, the inhibition of the binding by DTT implies that besides free sulfhydryl group(s), the integrity of a disulfide bridge is also important for [3H]CP-55,940 binding to the cannabinoid receptor.

Animals↗
PubMed1992

Sulfhydryl modification of E. coli Cpn60 leads to loss of its ability to support refolding of rhodanese but not to form a binary complex.

Differential chemical modification of E. coli chaperonin 60 (cpn60) was achieved by using one of several sulfhydryl-directed reagents. For native cpn60, the three cysteines were accessible for reaction with N-ethylmaleimide (NEM), while only two of them are accessible to the larger reagent 4,4'-dipyridyl disulfide (4-PDS). However, no sulfhydryl groups were modified when the even larger reagents 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) or 2-(4'-(iodoacetamido)anilino) naphthalene-6-sulfonic acid (IAANS), were employed, unless the chaperonin was unfolded. The cpn60 that had been covalently modified with NEM or IAANS, was not able to support the chaperonin-assisted refolding of the mitochondrial enzyme rhodanese, which also requires cpn10 and ATP hydrolysis. However, both modified forms of cpn60 were able to form binary complexes with rhodanese, as demonstrated by their ability to arrest the spontaneous refolding of the enzyme. That is, chemical modification with these sulfhydryl-directed reagents produced a species that was not prevented from interaction with partially folded rhodanese, but that was prevented from supporting a subsequent step(s) during the chaperonin-assisted refolding process.

Bacterial Proteins↗
PubMed1990

Evidence for the involvement of vicinal sulfhydryl groups in the insulin stimulation of intracellular glucose metabolism in Zajdela hepatoma cells.

Phenylarsine oxide (PhAsO), a dithiol reagent that blocks insulin stimulation of glucose transport in 3T3 L1 cells, also altered insulin stimulation of intracellular glucose metabolism in Zajdela Hepatoma cultured cells. PhAsO (2 microM) similarly inhibited the insulin-induced glycogen and lipid syntheses without modifying the basal level of these processes, cell viability or the ATP content. Prior incubation of the cells with PhAsO did not prevent insulin binding to the cells, or activation of the receptor tyrosine kinase, while it minimally (16%) altered receptor internalization. These results indicate that cellular dithiols located at a post-receptor step are involved in the transduction of the insulin signal to intracellular glucose metabolism.

Adenosine Triphosphate↗
PubMed1985

Water exchange through erythrocyte membranes: p-chloromercuribenzene sulfonate inhibition of water diffusion in ghosts studied by a nuclear magnetic resonance technique.

A comparison of water diffusion in human erythrocytes and ghosts revealed a longer relaxation time in ghosts, corresponding to a decreased exchange rate. However, the diffusional permeability of ghosts was not significantly different from that of erythrocytes. The changes in water diffusion following exposure to p-chloromercuribenzene sulfonate (PCMBS) have been studied on ghosts suspended in isotonic solutions. It was found that a significant inhibitory effect of PCMBS on water diffusion occurred only after several minutes of incubation at 37 degrees C. No inhibition was noticed after short incubation at 0 degree C, as previously used in some labelling experiments. This indicates the location in the membrane interior of the SH groups involved in water diffusion across human erythrocyte membranes. The nuclear magnetic resonance (n.m.r.) method appears as a useful tool for studying changes in water diffusion in erythrocyte ghosts with the aim of locating the water channel.

4-Chloromercuribenzenesulfonate↗
PubMed1978

[The indication of radiation treatment for irradiated chicken on the basis of the radiation--induced loss of protein sulfhydryl groups (author's transl)].

A spectrophotometric technique for the identification of irradiated chicken (gallus domesticus) and doses ranging between 0.1 and 2.5 Mrad is described. Spectrophotometric determination of the sulfhydryl content in the animal tissue before (control) and after using 6,6'-Dithiodinicotinic acid is applied. Ionizing radiation causes a permant loss of sulfhydryl groups in the animal tissue such as chicken. Irradiation at room temperature and storing at -18 degrees C over a period of approximately one month does not show restitution or repair of the sulfhydryl loss. The dose-effect relation for this radiation-induced decrease of the sulfhydryl content can be described best by a double exponential function. Irradiation conditions, preparation of protein suspension from chicken, spectrometric investigations and other experimental details are reported. The results of all will be discussed in detail.

Animals↗
PubMed1992

Intragastric nicotine protects against 40% ethanol-induced gastric mucosal injury despite pretreatment with propranolol or N-ethylmaleimide in rats.

We tested the hypotheses that the protective effect of intragastric nicotine against ethanol-induced gastric mucosal injury is dependent on propranolol- or N-ethylmaleimide-sensitive mechanisms. Propranolol was administered in doses (2 and 20 mg/kg) that provided dose-related blockade of beta-adrenoceptors (significant decreases in heart rate). N-Ethylmaleimide was administered in doses that previously had been shown to increase gastric vascular permeability (10 mg/kg) or inhibit gastric mucosal sulfhydryl compounds (50 mg/kg). At 0.5 hr after these or control subcutaneous pretreatments, the rats received intragastric nicotine (4 mg/kg) or vehicle. One hour later 40% ethanol was given intragastrically. The gastric corpus mucosal lesions were recorded by polaroid photographs after another hour, and their areas measured unbiasedly by computerized image analysis. The results showed that N-ethylmaleimide, but not propranolol, aggravated ethanol-induced gastric mucosal injury. The protective effect of intragastric nicotine was not modified by either pretreatment. We conclude that the mechanism mediating intragastric nicotine protection against 40% ethanol-induced gastric mucosal injury is independent of propranolol- or N-ethylmaleimide-sensitive mechanisms.

Animals↗
PubMed1989

Effects of mepirizole and basic antiinflammatory drugs on HCl-ethanol-induced gastric lesions in rats.

Mepirozole, a basic antiinflammatory drug and duodenal ulcerogen in laboratory animals, macroscopically protected the gastric mucosa of rats from HCl-ethanol-induced damage in a dose-dependent manner. These effects were evident when the agent was given orally, intraperitoneally, or subcutaneously at 3 or 10 mg/kg 0.5 hr before HCl-ethanol administration. Histologically, the surface epithelial and pit cells were not protected by mepirizole, but most of the mucosal cells located in the deeper portions were well preserved. Gastric acid secretion in the pylorus-ligated or acute fistula preparation was not affected by 10 mg/kg of mepirizole. Gastric motility determined by a balloon method was dose-dependently inhibited by the agent. Mepirizole protection was significantly reduced by pretreatment with subcutaneous indomethacin (5 mg/kg) and N-ethylmaleimide (10 mg/kg). The gastric motility inhibited by mepirizole was not reversed by indomethacin and N-ethylmaleimide treatment. These results suggest that the mechanism underlying mepirizole protection relates to both endogenous prostaglandins and sulfhydryl compounds present in the gastric mucosa, but does not relate to an inhibition of gastric motility. Dulcerozine and other basic antiinflammatory drugs (tiaramide, tinoridine, and benzydamine) given either orally or intraperitoneally at 10-100 mg/kg also dose-dependently prevented the development of HCl-ethanol-induced lesions. Mepirizole and other basic antiinflammatory drugs are cytoprotective in the rat stomach.

Animals↗
PubMed1995

Sporicidal action of peracetic acid and protective effects of transition metal ions.

Although peracetic acid (PAA) is used widely for cold sterilization and disinfection, its mechanisms of sporicidal action are poorly understood. PAA at high concentrations (5-10%) can cause major loss of optical absorbance and microscopically-visible damage to bacterial spores. Spores killed by lower levels of PAA (0.02-0.05%) showed no visible damage and remained refractile. Treatment of spores of Bacillus megaterium ATCC 19213 with PAA at concentrations close to the lethal level sensitized the cells to subsequent heat killing. In addition, PAA was found to act in concert with hypochlorite and iodine to kill spores. Antioxidant sulfhydryl compounds or ascorbate protected spores against PAA killing. Trolox, a water-soluble form of alpha-tocopherol, was somewhat protective, while other antioxidants, including alpha-tocopherol, urate, bilirubin, ampicillin and ethanol were not protective. Chelators, including dipicolinate, were not protective, but transition metal ions, especially the reduced forms (Co2+, Cu+ and Fe2+) were highly protective. The net conclusions are that organic radicals formed from PAA are sporicidal and that they may act as reducing agents for spores that are normally in a highly oxidized state, in addition to their well known actions as oxidizing agents in causing damage to vegetative cells.

Antioxidants↗
PubMed1979

Studies on lithium transport across the red cell membrane. VI. Properties of a sulfhydryl group involved in ouabain-resistant Na+-Li+ (and Na+-Na+) exchange in human and bovine erythrocytes.

The reactivity of the SH-group essential for ouabain-resistant Na+-Li+ (and Na+-Na+) exchange and its location within the membrane are studied on human and beef erythrocytes and beef red cell ghosts. N-ethylmaleimide (NEM), 1,6-hexane dimaleimide, and iodoacetamide can induce an irreversible, partial inhibition of Na+-Li+ exchange in erythrocytes of the two species. The development of the inhibition due to the alkylating agents is greatly accelerated by external Na+ and Li+. The inhibition takes 3 min (NEM) and 60 min (iodoacetamide) to come to completion in isotonic Na+ media, but is hardly detectable in choline+, K+ or Mg2+ media. The transport site of the exchange system and the site promoting NEM binding exhibit similar affinities for external Na+. The impermeable, monofunctional glutathione derivative of 1,6-hexane dimaleimide does not inhibit Na+-Li+ exchange. The mercurials PCMBS, PCMB, and Hg2+ inhibit Na+-Li+ exchange in beef, but not in human erythrocytes. The inhibitory action of PCMBS, being slightly accelerated by external Na+, is fully reversed by penetrating thiols such as 2-mercaptoethanol, whilst glutathione, an impermeable thiol, is ineffective. Pretreatment with PCMBS affords partial protection from the irreversible inhibition caused by NEM. Oxidation with copper orthophenanthroline inhibits Na+-Li+ exchange only when performed in the presence of penetrating thiols such as 2-mercaptoethanol. It is concluded that the SH-reagents studied inhibit Na+-Li+ exchange by modifying an essential SH-group of a membrane protein in such a way that the turnover number of the exchange system is reduced. This SH-group is separated from both the red cell exterior and interior by a penetration barrier and seems to be distinct from the cation binding site. The action of external Na+ and Li+ in promoting the reaction of alkylating inhibitors is interpreted to result from a conformational change of the transport protein induced by the binding of external Na+ or Li+.

4-Chloromercuribenzenesulfonate↗
PubMed1989

Inhibition of hexose transport in the human erythrocyte by 5, 5'-dithiobis(2-nitrobenzoic acid): role of an exofacial carrier sulfhydryl group.

The sulfhydryl reagent 5, 5'-dithiobis (2-nitrobenzoic acid) (DTNB) was used to study the functional role of an exofacial sulfhydryl group on the human erythrocyte hexose carrier. Above 1 mM DTNB rapidly inhibited erythrocyte 3-O-methylglucose influx, but only to about half of control rates. Efflux was also inhibited, but to a lesser extent. Uptake inhibition was completely reversed by incubation and washing with 10 mM cysteine, whereas it was only partially reduced by washing in buffer alone, suggesting both covalent and noncovalent interactions. The covalent thiol-reversible reaction of DTNB occurred on the exofacial carrier, since (i) penetration of DTNB into cells was minimal, (ii) blockade of potential uptake via the anion transporter did not affect DTNB-induced hexose transport inhibition, and (iii) DTNB protected from transport inhibition by the impermeant sulfhydryl reagent glutathione-maleimide-I. Maltose at 120 mM accelerated the covalent transport inhibition induced by DTNB, whereas 6.5 microM cytochalasin B had the opposite effect, indicating under the one-site carrier model that the reactive sulfhydryl is on the outward-facing carrier but not in the substrate-binding site. In contrast to glutathione-maleimide-I, however, DTNB did not restrict the ability of the carrier to reorient inwardly, since it did not affect equilibrium cytochalasin B binding. Thus, carrier conformation determines exposure of the exofacial carrier sulfhydryl, but reaction of this group may not always "lock" the carrier in an outward-facing conformation.

3-O-Methylglucose↗
PubMed1993

Effect of subchronic administration of antioxidants against cigarette smoke exposure in rats.

Effects of subchronic administration of antioxidants against pulmonary damage mediated by cigarette smoke were investigated in rats. Rats were continuously received ascorbic acid, N-acetylcysteine and ginseng extract together drinking water from day 25 after birth. After 30 days of antioxidant supplementation, rats were exposed to cigarette smoke generated from six cigarettes (11 mg tar) for 20 min per day throughout 30 days, and then several biochemical markers related to the redox status in vivo were analyzed in the respiratory system. The cigarette smoke induced mild histological changes in trachea and lungs. The activity of superoxide dismutase (SOD) in the lung was significantly increased, and catalase and glutathione peroxidase activities were increased less than SOD, but total sulfhydryl compounds (Total-SH) content was decreased by cigarette smoking. In spite of the increase in activities of antioxidant enzymes, the inhibitory capacity of lung preparations on in vitro lipid peroxidation using ox brain homogenates was decreased and the change in the capacity was not related to the changes of these intracellular enzymes activities, but with the content of Total-SH. On the other hand, the content of thiobarbituric acid reactive substances and the ratio of elastase to anti-protease in the lung homogenates were significantly increased. Supplementation of antioxidants, however, effectively attenuated all of such alterations induced by cigarette smoke. These results indicate that although cigarette smoking induces antioxidant enzymes in the lung as a self defense mechanism, it seems to be not sufficient to protect the pulmonary system, and that chronic antioxidant feeding could be effective to reduce pulmonary damage induced by free radicals.

Animals↗