Determination of L-glutathione by spot test and spectrophotometric methods based on its interaction with phenazine

This research paper presents simple and quick eco-friendly spot test and spectrophotometric methods for the determination of L-glutathione. The spot test assay is based on the formation of a color complex with phenazine methosulphate and L-glutathione on a thin-layer chromatography plate followed by image analysis using a scanner as a detector. For analysis, the image was converted into red, green, and blue (RGB) histograms. A series of parameters that influenced the color formation were investigated, and under the optimal conditions, a good linearity was observed in the range of 200-1000 μg mL^-1 and 249-1000 μg mL^-1 of L-glutathione with correlation coefficients of 0.9907 for B and 0.9903 for G channels. For the spectrophotometric method, a good linearity was obtained in the range of 2.1-60 μg mL^-1 of L-glutathione concentration with a correlation coefficient of 0.9961. A mechanism of the reaction of L-glutathione with phenazine was proposed and confirmed by Fourier transform infrared and mass spectroscopy.

Antimicrobial Efficacy of Salvadora persica Extracts on a Monospecies Biofilm on Orthodontic Brackets In Vitro

PURPOSE

The oral cavity is a rich ecosystem with a plethora of microorganisms, and different components of fixed orthodontic appliances may contribute to a shift in the balance of oral ecology. The purpose of this study was to investigate the antimicrobial potential of hexane and ethanol extracts of Salvadora persica on a monospecies biofilm model established on orthodontic brackets in vitro.

MATERIALS AND METHODS

Streptococcus mutans biofilm was formed on mini diamond orthodontic brackets following three days of anaerobic incubation at 37˚C. The bacterial cell viability of this biofilm was measured after their exposure to saline, hexane extract of S. persica, ethanol extract of S. persica and 0.2% chlorhexidine using 3-(4, 5-dimethylthiazol- 2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulphophenyl)-2H-tetrazolium (MTS) assay. On half of the brackets, the colony forming units (CFU) were counted. Both experiments were performed in triplicate.

RESULTS

The absorbance values obtained from the MTS reduction assay after exposure to the different test agents showed a decline in the bacterial cell viability of the S. mutans biofilm as follows: chlorhexidine (+)<hexane extract (S. persica, 5 mg/ml)<ethanol extract (S. persica, 5 mg/ml)<saline+2% DMSO (-). There was significant difference between saline+2% DMSO and the other test solutions (p<0.05). The mean absorbance values showed that the antimicrobial activity of hexane extract was slightly more effective than that of the ethanol extract and was nearly as effective as chlorhexidine (+). However, the differences in the absorbance values between the extracts of S. persica and chlorhexidine (+) were not statistically significant (p>0.05). The CFU counts of S. mutans obtained from chlorhexidine exposure were lower than from hexane and ethanol extracts.

CONCLUSION

S. persica extracts were found to have antimicrobial effects on S. mutans biofilm established in vitro on orthodontic brackets suggestive of its potential use as an oral antimicrobial agent for orthodontic patients.

Neonatal disruption of serine racemase causes schizophrenia-like behavioral abnormalities in adulthood: clinical rescue by d-serine

BACKGROUND

D-Serine, an endogenous co-agonist of the N-methyl-D-aspartate (NMDA) receptor, is synthesized from L-serine by serine racemase (SRR). Given the role of D-serine in both neurodevelopment and the pathophysiology of schizophrenia, we examined whether neonatal disruption of D-serine synthesis by SRR inhibition could induce behavioral abnormalities relevant to schizophrenia, in later life.

METHODOLOGY/PRINCIPAL FINDINGS

Neonatal mice (7-9 days) were injected with vehicle or phenazine methosulfate (Met-Phen: 3 mg/kg/day), an SRR inhibitor. Behavioral evaluations, such as spontaneous locomotion, novel object recognition test (NORT), and prepulse inhibition (PPI) were performed at juvenile (5-6 weeks old) and adult (10-12 weeks old) stages. In addition, we tested the effects of D-serine on PPI deficits in adult mice after neonatal Met-Phen exposure. Finally, we assessed whether D-serine could prevent the onset of schizophrenia-like behavior in these mice. Neonatal Met-Phen treatment reduced D-serine levels in the brain, 24 hours after the final dose. Additionally, this treatment caused behavioral abnormalities relevant to prodromal symptoms in juveniles and to schizophrenia in adults. A single dose of D-serine improved PPI deficits in adult mice. Interestingly, chronic administration of D-serine (900 mg/kg/day from P35 to P70) significantly prevented the onset of PPI deficits after neonatal Met-Phen exposure.

CONCLUSIONS/SIGNIFICANCE

This study shows that disruption of D-serine synthesis during developmental stages leads to behavioral abnormalities relevant to prodromal symptoms and schizophrenia, in later life. Furthermore, early pharmacological intervention with D-serine may prevent the onset of psychosis in adult.

Ultrasonic imaging of endothelial CD81 expression using CD81-targeted contrast agents in in vitro and in vivo studies

This study is designed to investigate the feasibility for molecular imaging of endothelial CD81 expression in vitro and in vivo using the CD81-targeted ultrasound contrast agents (UCA). In the in vitro study, murine bEnd.3 cells were stimulated with phenazine methosulfate (PMS), an oxidative stress inducer. Changes in CD81 expression after stimulation were confirmed by Western blotting, tracked by using the targeted UCA and further imaged under ultrasound imaging system with 5 MHz transmit frequency. In the in vivo study, expression of endothelial CD81 proteins in murine carotid artery vessels was studied using high-frequency ultrasound system with 40 MHz transmit frequency. Our results showed that endothelial CD81 expression was gradually up-regulated with the increase of PMS concentration. Correspondingly, the accumulation of targeted UCA was gradually improved and could be inhibited significantly upon addition of free anti-CD81 antibodies. The mean video intensity (grey-level) of stimulated cells and vessels from backscatter of the CD81-targeted UCA was 17.2 (interquartile range [IQR] 15.4-19.8) and 27.2 (IQR 22.4-29.8), significantly greater than that of non-stimulated cells with 9.0 (IQR 8.6-10.8) (p < 0.01) and non-stimulated vessels with 11.3 (IQR 10.4-13.2) (p < 0.01), respectively. In conclusion, CD81-targeted UCA allows noninvasive assessment of the expression levels of CD81 on the vascular endothelium and may provide potential insights into early atherosclerotic plaque detection and treatment monitoring.

New and simple plate test for screening relative transfructosylation activity of fungi

Several microorganisms are reported to have transfructosylation activity due to fructosyltransferase and/or fructofuranosidase activities. However, the search for other fungi with higher transfructosylation activity remains a challenge. So, a presumptive and indirect colorimetric plate assay for the evaluation of transfructosylation activity in fungi was developed which involved the simultaneous determination in the same plate of glucose and fructose released from sucrose. The method entailed the (a) glucose oxidase-peroxidase coupled reaction using phenol and 4-aminoantipyrine for determination of glucose; and (b) fructose dehydrogenase oxidation in the presence of a tetrazolium salt for determination of fructose. The presence of enzymes with transfructosylation activity was identified by the formation of pink (presence of glucose) and blue (presence of fructose) halos around the fungal colony. In conclusion, the results showed that the method is suitable for screening a large number of fungi due to its simplicity, reproducibility and rapidity and also gives a relative quantitative idea of the transfructosylation activity of different fungi species.

Rapid epidemiologic assessment of glucose-6-phosphate dehydrogenase deficiency in malaria-endemic areas in Southeast Asia using a novel diagnostic kit

We recently reported a new rapid screening method for glucose-6-phosphate dehydrogenase (G6PD) deficiency. This method incorporates a new formazan substrate (WST-8) and is capable of detecting heterozygous females both qualitatively and quantitatively. Here, we report its evaluation during field surveys at three malaria centres and in malaria-endemic villages of Myanmar and Indonesia, either alone or in combination with a rapid on-site diagnosis of malaria. A total of 57 severe (45 males and 12 females) and 34 mild (five males and 29 females) cases of G6PD deficiency were detected among 855 subjects in Myanmar whilst 30 severe (25 males and five females) and 23 mild (six males and 17 females) cases were found among 1286 subjects in Indonesia. In all cases, severe deficiency was confirmed with another formazan method but due to limitations in its detection threshold, mild cases were misdiagnosed as G6PD-normal by this latter method. Our results indicate that the novel method can qualitatively detect both severely deficient subjects as well as heterozygous females in the field. The antimalarial drug, primaquine, was safely prescribed to Plasmodium vivax-infected patients in Myanmar. Our new, rapid screening method may be essential for the diagnosis of G6PD deficiency particularly in rural areas without electricity, and can be recommended for use in malaria control programmes.

Cytokinin oxidase/cytokinin dehydrogenase assay: optimized procedures and applications

Spectrophotometric methods for determining the activity of cytokinin oxidase/cytokinin dehydrogenase (EC 1.5.99.12) were developed and optimized. A sensitive end-point method based on a combination of the electron acceptor 2,6-dichlorophenolindophenol and Schiff base formation of the reaction product with 4-aminophenol under acidic conditions can be applied to crude cell and tissue extracts. The assay was also adapted for other substrates than N6-(2-isopentenyl)adenine, such as zeatin and the aromatic cytokinins, although an enzyme which degrades the latter compounds has not yet been identified. The second novel method is an initial rate method based on the coupled redox reaction of phenazine methosulfate and 3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide resulting in the formation of a formazan dye. This method can be used for kinetic studies with purified enzyme and is entirely substrate independent.

Development of an XTT tetrazolium salt-based assay for detection of specific hyperthermia sensitizers in a high-flux screening programme

It is now possible to search for new drugs using high-throughput screening of chemical libraries accumulated over the past few years. To detect potential new hyperthermia sensitizers, we are screening for chemical inhibitors of thermotolerance. For the screening of a large chemical library, a rapid and simple assay based on the XTT-tetrazolium salt with the addition of intermediate electron acceptor, phenazine methosulphate (PMS) as a promoter, was developed. It was found that the sensitivity of the XTT/PMS assay is sufficient for assessing thermal cell killing and thermotolerance, although it was highly dependent on cell number and type. When the formazan assay system was challenged with the bioflavonoid drug quercetin (up to 25mm) and validated against the clonogenic cell survival assay, significant decreases in thermotolerant cell viability were observed, directly reflecting inhibition of thermotolerance. Although short-term assays can, in some instances, underestimate overall cell killing, the dose dependency of inhibition of thermotolerance by quercetin recorded in this study by clonogenic and XTT/PMS assays was similar. Application of the XTT/PMS assay in chemical library screening was highly effective in differentiating potential thermotolerance inhibitors from both chemicals with lack of efficacy and from toxic compounds. Taken together, these results show that the XTT/PMS assay, when carried out under careful conditions, is well suited for primary high-flux screen of many thousands of compounds, thus opening up new areas for discovery of hyperthermia sensitizers.

Scavenger effect of experimental and clinically used cardiovascular drugs

Oxygen free radicals play an important role in several physiologic and pathophysiologic processes. In pathophysiologic circumstances they can modify and damage biologic systems. Their functional properties (exposed to high oxygen tension) place red blood cells among the most susceptible cells to the harmful effect of free radicals. Because oxygen free radicals are involved in a wide range of diseases, scavenging these radicals should be an important therapeutic approach. In this study the antioxidant capacities of experimental and clinically used cardiovascular drugs were investigated. Phenazine methosulfate was used to generate free radicals and thus harden red blood cells. Filtration technique and potassium leaking were used to detect the scavenging effect of the examined drugs. The experimental drug H-2545 provided 43% protection against phenazine methosulfate-induced changes in red blood cell filterability (p < 0.001). Although some of the examined, clinically used cardiovascular drugs (carvedilol, metoprolol, verapamil, trimetazidine) also showed significant (p < 0.05) antioxidant effect, they were less efficient than H-2545. The scavenger effect of this novel drug exceeded the antioxidant properties of vitamin E. Modification of mexiletine with a pyrroline ring significantly improved its antioxidant capacity, suggesting that this molecular segment is responsible for the antioxidant effect.

Quorum sensing in Pseudomonas aeruginosa controls expression of catalase and superoxide dismutase genes and mediates biofilm susceptibility to hydrogen peroxide

Quorum sensing (QS) governs the production of virulence factors and the architecture and sodium dodecyl sulphate (SDS) resistance of biofilm-grown Pseudomonas aeruginosa. P. aeruginosa QS requires two transcriptional activator proteins known as LasR and RhlR and their cognate autoinducers PAI-1 (N-(3-oxododecanoyl)-L-homoserine lactone) and PAI-2 (N-butyryl-L-homoserine lactone) respectively. This study provides evidence of QS control of genes essential for relieving oxidative stress. Mutants devoid of one or both autoinducers were more sensitive to hydrogen peroxide and phenazine methosulphate, and some PAI mutant strains also demonstrated decreased expression of two superoxide dismutases (SODs), Mn-SOD and Fe-SOD, and the major catalase, KatA. The expression of sodA (encoding Mn-SOD) was particularly dependent on PAI-1, whereas the influence of autoinducers on Fe-SOD and KatA levels was also apparent but not to the degree observed with Mn-SOD. beta-Galactosidase reporter fusion results were in agreement with these findings. Also, the addition of both PAIs to suspensions of the PAI-1/2-deficient double mutant partially restored KatA activity, while the addition of PAI-1 only was sufficient for full restoration of Mn-SOD activity. In biofilm studies, catalase activity in wild-type bacteria was significantly reduced relative to planktonic bacteria; catalase activity in the PAI mutants was reduced even further and consistent with relative differences observed between each strain grown planktonically. While wild-type and mutant biofilms contained less catalase activity, they were more resistant to hydrogen peroxide treatment than their respective planktonic counterparts. Also, while catalase was implicated as an important factor in biofilm resistance to hydrogen peroxide insult, other unknown factors seemed potentially important, as PAI mutant biofilm sensitivity appeared not to be incrementally correlated to catalase levels.

Visualization of the enzyme trimethylamine oxide demethylase in isoelectric focusing gels by an enzyme-specific staining method

An enzyme-specific staining method for trimethylamine oxide demethylase (TMAO-ase) was developed. Direct visualization could be reached by coupling the reactions of the specific TMAO-ase assay with another reaction step generating as final product a dark-blue formazan. For these purposes 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) as tetrazolium salt and phenazine methosulfate (PMS) as electron transfer substance were used. Clear, dark-blue colored bands could be detected on 300 microm isoelectric focusing gels (IEF). Comparisons of enzyme-stained and protein-stained gels showed that diffusion could not be observed and that the band pattern of TMAO-ase could also be seen in the protein stain. The pI range where TMAO-ase was located was 5.6-6.6 for extracts and 6.2-6.6 for partially purified TMAO-ase. Specificity of stained TMAO-ase bands was assessed by the preparation of staining solution without the substrate trimethylamine oxide (TMAO) and by extraction of TMAO-ase from the gel and performance of the specific TMAO-ase assay.

Formalin fixation in the cytochemical demonstration of succinic dehydrogenase of mitochondria

A variety of established methods for protecting mitochondria were tested on rat duodenal epithelium during the histochemical assay for succinic dehydrogenase. The use of sucrose at isotonic or hypertonic concentrations, 7.5 per cent polyvinylpyrrolidone, divalent cations, physiological salt solutions, phenazine methosulfate, coenzyme Q₁₀, and menadione failed to improve the quality of the histochemical preparation once fresh frozen sections were prepared. However, preservation of mitochondrial integrity with little diminution in succinic dehydrogenase activity was obtained by fixing tissue slices (less than 1 mm. in thickness) in 8 per cent unneutralized, aqueous formaldehyde from 8 to 16 minutes at from 5° to 10°C. prior to freezing. To offset the inhibition of enzymatic activity it was necessary to extend the incubation period by 10 to 15 minutes. Two-micron-thick sections were easily obtained from the frozen blocks of such fixed tissue and incubated in the unmodified Nitro—BT-succinate medium. Once the optimum conditions for fixation of intestinal epithelium were determined, many other tissues were subjected to the same procedure. From the morphological standpoint the appearance of the mitochondria in these histochemical preparations compares favorably with the results obtained using the classical Regaud iron-hematoxylin staining procedure. With most tissues, the results are superior to those with fresh frozen sections. However, results with muscle, sperm, and kidney tubular epithelium are not as strikingly improved as with gut and liver.

Protective action of some Cu(II) complexes against photohemolysis induced by m. chloroperbenzoic acid

m. Chloroperbenzoic acid (CPBA) was used as a photosensitizer in the photolysis of human red blood cells. Treatment of the cells with 25, 50 100, or 200 microM CPBA produced 3.5%, 85.9%, 252.6% or 350.9% photohemolysis, respectively, compared with untreated control cells. Some copper (II) complexes [CuL2] with SOD-like activity containing 2-methyl amino pyridine and various anions (Cl-, Br-, NO3-, ClO4-, or SO4--) were tested for their protective efficiency toward the cell damage photoinduced by CPBA. Treatment of the cells with maximum dose (200 microM) Cu(II), bromide, chloride, nitrate, sulfate, or perchlorate complexes with 2-methyl amino pyridine produced 85.87%, 59.28%, 49.29%, 33.47%, or 23.80% protection, respectively, against the cells irradiated without addition of Cu(II) complexes. A mechanism involving oxygen radicals and sensitizer photodegradation products was suggested to interpret the results.

THE EFFECT OF MENADIONE AND PHENAZINE METHOSULFATE ON THE TETRAZOLIUM REDUCTION SYSTEM UNDER HISTOCHEMICAL CONDITIONS

The influence of phenazine methosulfate and menadione on the activity of DPNH- and TPNH-tetrazolium reductase, succinic, lactic, and triphosphopyridine nucleotide-linked isocitric dehydrogenase were studied with reference to applied histochemistry. Fresh frozen sections of various tissues were employed in conjunction with nitro blue tetrazolium as the hydrogen acceptor.

Phenazine methosulfate was found to produce a variable effect upon staining, enhancing it or suppressing it according to incubation conditions. Suppression was most pronounced with higher concentrations. Menadione had no suppressive influence and was useful in increasing tetrazolium reduction. Its usefulness is, however, limited unless a soluble factor, possibly DT-(DPNH-TPNH)-diaphorase, can be prevented from diffusing into the medium, and "nothing dehydrogenase" is selectively inactivated.

Microplate superoxide dismutase assay employing a nonenzymatic superoxide generator

The antioxidant enzyme superoxide dismutase (EC 1.15.1.1) (SOD) catalyzes the conversion of superoxide anion radical (O2.-) to hydrogen peroxide and molecular oxygen. SOD helps prevent tissue damage by O2.- and its metabolites, and augmentation of tissue SOD is a useful therapeutic strategy in certain diseases having an oxidative-injury component. Routine application of direct SOD assays is not technically facile, since the short half-life of the O2.- substrate and its free radical nature necessitate specialized analytical equipment to detect and measure O2.- chemically. Consequently, indirect SOD assays which monitor some change in an indicator substance reacting with O2.- are routinely used, particularly for biological samples. Limitations of indirect test systems utilizing heme-based indicators for the presence of O2.- and/or enzymatic O2.- generators led us to develop a SOD microassay based on spectrophotometric assessment of O2.- mediated nitro blue tetrazolium reduction by an aerobic mixture of NADH and phenazine methosulfate, which produces superoxide chemically at nonacidic pH (Rao, Free Radical Biol. Med. 7, 513-519, 1989). The proposed SOD assay system is formatted for use in an automated 96-well microplate reader and has the virtues of a nonheme indicator, a nonenzymatic O2.- source, physiological pH, and economy of time and materials. The assay has been applied to measure purified and tissue SOD (Cu,Zn- and Mn-types) activity as well as O2.- turnover by small-molecule "SOD mimetics."

Use of hydrophobic chromatography for purification of the membrane-located choline dehydrogenase from a Pseudomonas strain

Choline dehydrogenase has been purified using hydrophobic chromatography 250-fold from a Pseudomonas strain. Although the enzyme is associated with the cell membrane and could be extracted from membrane preparations, it was best purified from a complete cell extract made with a non-ionic detergent. Only phenazine methosulfate was able to act as electron acceptor; there was no evidence of bound flavin, but there was evidence of pyrroloquinoline quinone cofactor. The purified enzyme had a specific activity of up to 67 units/mg, which is at least ten times higher than the values reported for mitochondrial choline dehydrogenases, and up to 100 times higher than previous reports for the Pseudomonas enzyme. The estimated subunit size of 66 kDa, which corresponds with the native size, is close to that deduced from the gene sequence of the Escherichia coli betA gene, and preliminary N-terminal sequencing shows homology with this deduced sequence. The next enzyme in the degradation pathway of choline, betaine aldehyde dehydrogenase, was also purified from the same extract.

Evaluation of a new cytotoxicity assay for Clostridium perfringens type D epsilon toxin

A new cytotoxicity assay for determining the activity of epsilon toxin produced by Clostridium perfringens type D has been developed. Viability of cultured cells was determined by the ability of only live cells to convert 5-(3-carboxymethoxyphenyl)-2-(4,5-dimethylthiazolyl)-3-(4- sulfophenyl)tetrazolium to the coloured product formazan in the presence of phenazine methosulfate. Of the 12 cell lines tested, only the MDCK cell line was susceptible to epsilon toxin. Specificity was confirmed by the ability of only specific monoclonal antibodies to inhibit cytotoxicity. Good correlation was obtained with the mouse lethality assay (r = 0.991) and over a wide range of viability (15-75%) as determined by ethidium bromide/acridine orange staining (r = 0.995).

Reactive oxygen species involved in phenazine-methosulfate-induced rat lens opacification. An experimental model of cataract

The excised rat crystalline lens opacified when incubated aerobically with phenazine methosulfate, but no opacification was observed under anaerobic conditions. Morphological studies revealed development of opacification in the cortex. The opacification resembled that often seen in the early period of senile cataract as well as in naphthalene-induced and UV cataract. Both an increase in hydration and in electrolyte imbalance accompanied this opacification. Na,K-ATPase activity of the opacified lens was found to decrease. In order to investigate if activated oxygen is involved in these processes, we conducted an electron spin resonance study by means of a spin trapping technique. When the lens homogate was incubated with phenazine methosulfate, OH radicals were generated under aerobic but not under anaerobic conditions. Reduced pyridine nucleotides must be involved in the process, because the mixture of nicotinamide adenine dinucleotide phosphate [NAD(P)] and phenazine methosulfate did not generate OH radicals, but the mixture of NAD(P)H and phenazine methosulfate generates OH radicals, indicating that reduced phenazine methosulfate was involved in the OH radical generation. Probably, the generated OH radicals inactivated Na,K-ATPase residing in the epithelium of the lens, which eventually caused opacification of the lens. The present experiment system may be used for the elucidation of lens opacification (cataract) involved with reactive oxygen species.

Effect of covalent binding of a derivative of 2',3'-O-(2,4,6-trinitrophenyl)-ADP to the tight binding site of CF1 on the enzyme activity

Irradiation of isolated chloroplast thylakoids with TNP-ADP results in non-covalent binding and covalent incorporation of a reaction product of TNP-ADP formed by photosynthetic reduction into the so-called "tight" nucleotide binding site of CF1 [Ponse et al. (1992) Z. Naturforsch. 47c, 264-274]. CF1 extracted from thus-loaded thylakoid membranes yielded maximal incorporation of 1 mol/mol of CF1. Almost half had the covalent bond with CF1. In experiments with TNP-[14C]ADP, radioactivity was detected almost equivalently on alpha and beta subunits, suggesting that the binding site may be at the interface between alpha and beta subunits. Enzyme activities of the thylakoid membrane-bound enzyme after covalent labeling were measured. Inhibition, ranging from 20 to 25%, was less than expected from the percentage of CF1 molecules labeled (40-50%). It is suggested that only half of the labeled enzymes, probably those with the nucleotide analog linked to the beta subunit, are inactive.

Electrochemical bioreactor with immobilized glucose-6-phosphate dehydrogenase on the rotating graphite disc electrode modified with phenazine methosulfate

Physical adsorption, covalent binding through the carbodiimide reaction between the surface carboxyl group and the amino group of the protein, and the crosslinking method with bovine serum albumin by glutaraldehyde were applied for the immobilization of glucose-6-phosphate dehydrogenase (G6PDH) on a graphite electrode. Among those, the crosslinking method was employed for its highest apparent enzyme activity per unit surface area. Phenazine methosulfate (PMS), as a mediator for the electrochemical oxidation of NADH, was also immobilized on the graphite surface through adsorption. The conjugation reaction of G6PDH and the electrochemical oxidation of NADH were confirmed by cyclic voltammetry and the constant potential electrochemical reaction. An electrochemical bioreactor system was established by using a rotating disc graphite electrode with G6PDH immobilized. The coenzyme, NAD, was effectively recycled between the electrochemical and the enzymatic reactions.

Native polyacrylamide gel electrophoresis of membrane proteins: glutaminase detection after in situ specific activity staining

A new procedure for the analysis and detection of phosphate-activated glutaminase (EC 3.5.1.2) by native electrophoresis has been developed. The method is based on the in situ detection of glutaminase activity in two different systems of native polyacrylamide gradient gels, containing 3-(3-cholamidopropyl)-dimethyl-ammonio-1-propane sulfonate (CHAPS) or Triton X-100 as nondenaturant detergents. Crude Triton X-100 extracts of mitochondria were resolved by electrophoresis. The enzyme was specifically revealed by incubation of the gel with glutamine and coupling the oxidation of the glutamate formed to the reduction of a tetrazolium dye, in the presence of glutamate dehydrogenase trapped in a 1% agar solid overlay. Both Ehrlich ascitic cell and mouse kidney glutaminases were resolved by native electrophoresis and specifically detected with the activity staining. Moreover, the redox-cycling staining was tested in solution, showing linearity with the amount of glutamate or glutaminase activity present. The method described could be a useful tool for native polyacrylamide gel electrophoresis of membrane proteins.

Purification of sn-glycerol-3-phosphate dehydrogenase from Trypanosoma brucei brucei

A protein has been purified from the membranes of bloodstream forms of Trypanosoma brucei brucei. The purified material contained a single polypeptide chain of molecular mass 67 kilodaltons as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis; under "native" conditions it migrated through a Sephacryl S-300 column with a similar molecular mass. The purified protein catalysed electron transfer from sn-glycerol 3-phosphate to oxygen with the subsequent formation of water. Electron transfer by the purified enzyme to O2 was dependent on the presence of low concentrations of the mediator phenazine methosulfate. This protein is clearly the major membrane-bound sn-glycerol-3-phosphate dehydrogenase, but it also has some characteristics suggestive of the trypanosome alternative oxidase activities.

Mediated amperometric determination of xylose and glucose with an immobilized aldose dehydrogenase electrode

An enzyme electrode was constructed for amperometric determination of xylose and glucose. The electrode is based on the PQQ-dependent membrane-bound aldose dehydrogenase (ALDH) from Gluconobacter oxydans. ALDH was covalently immobilized on a graphite electrode. Immobilized dimethylferrocene, soluble ferrocene carboxylic acid and phenazine methosulphate were used as electron transfer mediators. When xylose was measured electrochemically using an electrode modified with ALDH and dimethylferrocene, the linear measurement range extended to 100 mM. For glucose measurement the linear measurement range was about one-tenth of that for xylose. The electrode showed fairly good stability; 50% of the original electrode response was still obtained after 5 days of intermittent use. The effect of possible leakage of adsorbed mediator was determined by measuring the response of an electrode with soluble mediator as a function of time. The reproducibility of the electrode was good, the standard deviation of the electrode response in ten measurements with the same electrode being only 2.7%.

An improved colorimetric assay for cell proliferation and viability utilizing the tetrazolium salt XTT

A new tetrazolium salt XTT, sodium 3'-[1-[(phenylamino)-carbonyl]-3,4-tetrazolium]-bis(4-methoxy-6- nitro)benzene-sulfonic acid hydrate, was evaluated for use in a colorimetric assay for cell viability and proliferation by normal activated T cells and several cytokine dependent cell lines. Cleavage of XTT by dehydrogenase enzymes of metabolically active cells yields a highly colored formazan product which is water soluble. This feature obviates the need for formazan crystal solubilization prior to absorbance measurements, as required when using other tetrazolium salts such as MTT. Bioreduction of XTT by all the murine cells examined was not particularly efficient, but could be potentiated by addition of electron coupling agents such as phenazine methosulfate (PMS) or menadione (MEN). Optimal concentrations of PMS or MEN were determined for the metabolism of XTT by the T cell lines HT-2 and 11.6, NFS-60 a myeloid leukemia, MC/9 a mast cell line and mitogen activated splenic T cells. When used in combination with PMS, each of these cells generated higher formazan absorbance values with XTT than were observed with MTT. Thus the use of XTT in colorimetric proliferation assays offer significant advantages over MTT, resulting from reduced assay time and sample handling, while offering equivalent sensitivity.

Use of an aqueous soluble tetrazolium/formazan assay for cell growth assays in culture

A new tetrazolium analog of 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) was evaluated as a substitute for MTT in the microculture screening assay for in vitro cell growth. This new tetrazolium compound, 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2- (4-sulfophenyl)-2H-tetrazolium, inner salt (MTS), in the presence of phenazine methosulfate (PMS), gave a water-soluble formazan product that had an absorbance maximum at 490-500 nm in phosphate-buffered saline. The amount of colored product formed was proportional to the number of cells and the time of incubation of the cells with MTS/PMS. MTS/PMS was reactive in all the cell lines tested which included mouse leukemia L1210 cells, mouse Ehrlich tumor cells, mouse 3T3 fibroblasts, and human colon tumor cells (HT-29). HT-29 and 3T3 fibroblasts reduced MTS/PMS more efficiently than they reduced MTT. Comparable to the amount of product formed from MTT, MTS/PMS gave excellent product formation. The IC50 value for pyrazoloimidazole obtained using MTS/PMS was 200 microM; for 5-fluoro-2'-deoxyuridine, the IC50 value was 0.9 nM. These values compared very favorably with the IC50 values obtained by direct cell counts. Further, the same IC50 values were obtained when the absorbances of the formazan product in the 96-well plates were determined after different times of incubation.

Microphotometric determination of enzymes in brain sections. IV. Isocitrate dehydrogenases

A polyvinyl alcohol-(PVA) containing incubation medium was adapted for the microphotometric determination (kinetic and end-point measurements) of the activities of NAD- and NADP-linked isocitrate dehydrogenases (ICDHs) in cryostat sections of the rat hippocampus. The following incubation medium is recommended for the quantification of NAD- and NADP- (differences in brackets) ICDHs: 100 mM DL-isocitrate, 10 mM sodium azide, 5 mM (4 mM) nitroblue tetrazolium (NBT), 7 mM NAD (4 mM NADP), 10 mM magnesium chloride, 0.25 mM phenazine methosulfate (PMS), with or without 5 mM ADP (without ADP), 23% PVA in 0.05 M Hepes buffer; the final pH was 7.5. With these incubation media a linear response of the reactions lasted at least 20 min. In kinetic and end-point measurements the same level of activities was demonstrable. The use of NaN3 (as a blocker of the respiratory chain) and PMS (as artificial electron carrier) was indispensible for the transfer of all reduction equivalents in the dehydrogenase reactions to the tetrazolium salt NBT. Furthermore, the activation by magnesium ions and the need of PVA to avoid diffusion artefacts of the loosely bound ICDHs were clearly shown. It is concluded that the quantification of ICDHs in situ could be a valuable tool for neurochemical investigations because ICDHs play a role not only in the substrate flux through the tricarboxylic acid cycle but also in providing alpha-ketoglutarate for the formation of glutamate which is an important amino acid in the brain.

Microphotometric determination of enzymes in brain sections. V. Glycerophosphate dehydrogenases

An incubation medium was adapted for the microphotometric determination (kinetic and end-point measurements) of the activities of mitochondrial alpha-glycerophosphate dehydrogenase (GPDH) in the rat hippocampus. For comparison, the activities of the cytoplasmic NAD-linked alpha-glycerophosphate dehydrogenase were also measured. The study showed that in the demonstration of both enzymes the use of an exogenous electron carrier is necessary. Both enzymes react to phenazine methosulfate (PMS) which transfers reduction equivalents to the electron acceptor nitroblue tetrazolium chloride (NBT), thus causing a coreaction of GPDH in the demonstration of NAD-GPDH. Therefore, only the NAD-independent GPDH which is stimulated by menadione, can be selectively demonstrated in the histochemical procedure applied. The final incubation medium of GPDH consisted of 15 mM L-glycerol 3-phosphate, 5 mM NBT, 0.4 mM menadione, 7.5% polyvinyl alcohol in 0.5 M Hepes buffer, pH 8; the final pH of the incubation medium was 7.5. A linear response of the reaction lasted about 5 min. There was a linear relationship between section thickness and the formation of reaction product up to a section thickness of 14 microns. The apparent Km value at 25 degrees C was 0.6 mM. It is concluded that using menadione histochemical methods are suited to determine the mitochondrial GPDH activities in brain sections whereas using PMS a coreaction of GPDH takes place in the demonstration of NAD-GPDH, so that a histochemical quantification of NAD-GPDH cannot be recommended.

A cytochemical staining procedure for succinate dehydrogenase activity in pre-ovulatory mouse oocytes embedded in low gelling temperature agarose

We describe a cytochemical staining procedure for succinate dehydrogenase (SDH) activity in pre-ovulatory mouse oocytes. The oocytes were embedded in low gelling temperature agarose and treated with caffeine before cytochemical staining in the presence of nitro blue tetrazolium (NBT), phenazinemethosulfate (PMS), and succinate. This resulted in intense staining of the oocytes by formazan precipitate. The level of aspecific formazan production in the absence of succinate was very low. We applied the procedure to oocytes matured in vitro and found that the location of the formazan precipitate as a result of SDH activity correlated well with the location of mitochondria. The chromatin of the cytochemically stained oocytes could subsequently be analyzed by means of the DNA-specific fluorochrome DAPI. In pre-ovulatory oocytes, we found a correlation between chromatin organization and the location of mitochondria: in oocytes with an intact germinal vesicle the mitochondria were uniformly distributed in the cytoplasm, as shown by fine grains of formazan precipitate. In oocytes with condensed chromatin the mitochondria apparently had clustered, because the formazan precipitate was more coarse in these cells.

Histochemical and immunohistochemical evidence for hepatic zone 3 distribution of alcohol dehydrogenase in rats

The distribution of alcohol dehydrogenase in the hepatic acinus was examined by both histochemical and immunohistochemical approaches. The immunohistochemical method using anti-alcohol dehydrogenase antibody indicated zone 3 predominance of this enzyme in the hepatic acinus, whereas a conventional histochemical method showed slight zone 1 predominance. However, when the histochemical technique was improved by using 2% glutaraldehyde instead of formalin for fixation and by adding phenazine methosulfate (0.33 mmol/L) to the staining incubation mixture, this method also supported zone 3 predominance of alcohol dehydrogenase. Evidence for zone 3 distribution of alcohol dehydrogenase may be of value in elucidating the mechanism of zone 3 liver damage by alcohol.

Superoxide anion radical-independent pathway for reduction of tetrazolium salts in aerobic mixtures consisting of NADH and 5-methylphenazinium methyl sulfate in the presence of aqueous micelles of nonionic and cationic detergents

The effect of Triton X-100 and certain other nonionic as well as cationic detergents on 5-methyl-phenazinium methyl sulfate (PMS)-mediated reduction of tetrazolium salts was studied under aerobic conditions using an exogenous source of reducing equivalents, such as NADH or by generating NADPH through an enzymatic reaction. In the absence of detergents, 5,10-dihydro-5-methylphenazine (MPH), formed on reduction of 5-methylphenazinium cation (MP+) of PMS by NAD[P]H, was reoxidized allowing first the univalent reduction of molecular oxygen (O2) to the superoxide anion radical (O2-.) which, in turn, reduced tetrazolium salts. In the presence of detergents, however, a significant fraction of the PMS-mediated reduction of tetrazolium salts appeared to proceed without the intervention of O2-. The reasons for this were examined experimentally and it was suggested that the reduced phenazine (i.e., MPH), which is sparingly soluble in aqueous solutions, migrates into detergent micelles where tetrazolium salts are reduced in preference to O2. By lowering the pH and thereby facilitating the H+-mediated dismutation of O2-., it was possible to obtain the reduction of tetrazolium salts, mediated selectively and directly by MPH in the micellar pseudophase. Employing the technique of saturation analysis, further evidence was obtained that lends support for preferential reduction of tetrazolium salts (e.g., nitroblue tetrazolium chloride) to that of O2 by the micelle-bound MPH.

The involvement of superoxide anions in the nitro blue tetrazolium chloride reduction mediated by NADH and phenazine methosulfate

Oxygen inhibits competitively the reduction of nitro blue tetrazolium chloride (nitro BT) by NADH and phenazine methosulfate (PMS). The oxygen-dependent inhibition is stronger in the presence of superoxide dismutase, whereas cyanide counteracts the oxygen interference. On the other hand, the oxidation of NADH mediated by PMS and dioxygen is affected only marginally by superoxide dismutase and cyanide. Therefore, it is concluded that the involvement of superoxide anions occurs at the level of nitro BT reduction via a nitro blue tetrazolinyl radical, as has been suggested by Picker and Fridovich [1984) Arch. Biochem. Biophys. 228, 155-158) and not at the level of PMS oxidation. The inhibition of the oxygen interference in the nitro BT reduction by cyanide is dependent on the cyanide concentration, whereas in nitrogen cyanide has no effect on the reduction. It is caused by competition between cyanide and oxygen to reduce or oxidize the nitro BT radical to either formazan with concomitant cyanogen production or nitro BT, respectively. For the histochemical localization and analysis of electropherograms of NAD(P)+-dependent dehydrogenase activities, the interference of oxygen can be avoided by anaerobic incubations or by the use of 5 mM nitro BT when incubating aerobically.

Source of superoxide anion radical in aerobic mixtures consisting of NAD[P]H, 5-methylphenazinium methyl sulfate and nitroblue tetrazolium chloride

The source of superoxide anion radical (O2-.) in aerobic mixtures consisting of NAD[P]H, 5-methylphenazinium methyl sulfate (or its 1-methoxy derivative) and tetrazolium salt was investigated using superoxide dismutase (SOD), Mn(II), ferricytochrome-C, and epinephrine as probes. NAD[P]H + phenazine + O2 was found to reduce nitroblue tetrazolium, iodonitrotetrazolium, and thiazolyl blue in a manner sensitive to agents that dismutase O2-., viz., SOD and Mn(II). It also mediated the reduction of ferricytochrome-C, and augmented the autooxidation of epinephrine to the adrenochrome, without a tetrazolium salt present in the medium. The autooxidation of epinephrine, but not the reduction of ferricytochrome-C, was found to be sensitive to SOD. Nitroblue tetrazolium, either singly or in combination with SOD, did not stimulate the reduction of ferricytochrome-C. The oxidation of NADH, mediated by a catalytically low concentration of phenazine(+O2), was augmented two-fold by SOD. These observations are consistent with, and lend support to, a scheme of redox events (Scheme-3) wherein it is proposed that the source of O2-. in the NAD[P]H + phenazine + tetrazolium(+O2) system is the reduced phenazine, that the tetrazoinyl radical (a one-electron reduction product of tetrazolium) may not reduce O2 to O2-., that the redox reaction between semiquinone radicals of phenazine and O2 is reversible, and that the disproportionation of semiquinone radicals constitutes an important rate-limiting reaction in the expression of phenazine redox couple.

Redox-dependent subunit dissociation of Azotobacter vinelandii hydrogenase in the presence of sodium dodecyl sulfate

Hydrogenases catalyze the reversible activation of dihydrogen. We have previously demonstrated that the purified hydrogenase from the nitrogen-fixing microorganism Azotobacter vinelandii is an alpha beta dimer (98,000 Da) with subunits of 67,000 (alpha) and 31,000 (beta) daltons and that this enzyme contains iron and nickel. The enzyme can be purified anaerobically in the presence of dithionite in a fully active state that is irreversibly inactivated by exposure to O2. Analysis of this hydrogenase by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE) following boiling in SDS yields two protein staining bands corresponding to the alpha and beta subunits. However, when this enzyme was treated with SDS (25-65 degrees C) for up to 30 min under anaerobic/reductive conditions and then analyzed by anaerobic SDS-PAGE, a protein staining band corresponding to an apparent molecular mass of 58,000 Da was observed that stained for hydrogenase activity. Analysis of the 58,000-Da activity staining band by a Western immunoblot or a second aerobic SDS-polyacrylamide gel revealed that this protein actually consisted of both the alpha and beta subunits. Thus, the activity staining band (apparent 58,000 Da) represents the 98,000-Da dimer migrating abnormally on SDS-PAGE. Treatment of the anaerobically purified hydrogenase with SDS under aerobic conditions or under anaerobic conditions with electron acceptors prior to electrophoresis resulted in no activity staining band and the separated alpha and beta subunits. A. vinelandii hydrogenase was also purified under aerobic conditions in an inactive O2 stable form that can be activated by removal of oxygen followed by addition of reductant. This enzyme (as isolated), the activated form, and the reoxidized form were analyzed for their stability toward denaturation by SDS. We conclude that the dissociation of the A. vinelandii hydrogenase subunits in SDS is controlled by the redox state of the enzyme suggesting an important role of one or more redox sites in controlling the structure of this enzyme.

The effect of complex formation upon the reduction rates of cytochrome c and cytochrome c peroxidase compound II

The effect of complex formation between ferricytochrome c and cytochrome c peroxidase (Ferrocytochrome-c:hydrogen peroxide oxidoreductase, EC 1.11.1.5) on the reduction of cytochrome c by N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD), reduced N-methylphenazonium methosulfate (PMSH), and ascorbate has been determined at low ionic strength (pH 7) and 25 degrees C. Complex formation with the peroxidase enhances the rate of ferricytochrome c reduction by the neutral reductants TMPD and PMSH. Under all experimental conditions investigated, complex formation with cytochrome c peroxidase inhibits the ascorbate reduction of ferricytochrome c. This inhibition is due to the unfavorable electrostatic interactions between the ascorbate dianion and the negatively charged cytochrome c-cytochrome c peroxidase complex. Corrections for the electrostatic term by extrapolating the data to infinite ionic strength suggest that ascorbate can reduce cytochrome c peroxidase-bound cytochrome c faster than free cytochrome c. Reduction of cytochrome c peroxidase Compound II by dicyanobis(1,10-phenanthroline)iron(II) (Fe(phen)2(CN)2) is essentially unaffected by complex formation between the enzyme and ferricytochrome c at low ionic strength (pH 6) and 25 degrees C. However, reduction of Compound II by the negatively changed tetracyano-(1,10-phenanthroline)iron(II) (Fe(phen)(CN)4) is enhanced in the presence of ferricytochrome c. This enhancement is due to the more favorable electrostatic interactions between the reductant and cytochrome c-cytochrome c peroxidase Compound II complex then for Compound II itself. These studies indicate that complex formation between cytochrome c and cytochrome c peroxidase does not sterically block the electron-transfer pathways from these small nonphysiological reductants to the hemes in these two proteins.

Nitrate reductase activity test: phenazine methosulfate-ferricyanide stop reagent replaces postassay treatment

Nitrate reductase activity is usually measured by colorimetric determination of the nitrite formed. Since reduced pyridine nucleotides interfere with color formation, the use of NADPH or NADH in the assay requires a specific postassay treatment to remove excess substrate. A "stop mix" containing 1.5 mM phenazine methosulfate and 4.0 mM ferricyanide (final concentrations 0.136 and 0.36 mM, respectively) can remove excess NAD(P)H and terminate the enzymatic reaction quickly in a single, time-saving step. For activity tests containing dithionite we recommend the use of a 1:1 mixture of the two color reagents to avoid incomplete color formation. This may occur during longer time intervals between addition of the color reagents due to destruction of the diazonium salt formed with the first reagent by oxidation product(s) of dithionite.

Hydrogenase activities in cyanobacteria

In the unicellular Anacystis nidulans, the expression of both the H2-uptake (with phenazine methosulfate or methylene blue as the electron acceptor) and H2-evolution (with methyl viologen reduced by Na2S2O4) was dependent on Ni in the culture medium. In extracts from Anacystis and Anabaena 7119, H2-evolution and uptake activities were strongly inhibited by Cu2+, p-chloromercuribenzoate and HgCl2 suggesting that at least one functional SH-group is involved in catalysis by hydrogenase. Extracts from the N2-fixing Anabaena 7119 contained two different hydrogenase fractions which could be separated by chromatography on DE-52 cellulose using a linear NaCl concentration gradient. The fraction eluting with 0.13 M NaCl from the column catalyzed only the uptake of H2 with methylene blue as the electron acceptor but virtually not the evolution of H2 ("uptake" hydrogenase fraction). The fraction eluting at a NaCl strength of 0.195 M catalyzed both H2-uptake with methylene blue and H2-evolution with reduced methyl viologen ("reversible" hydrogenase fraction). Growth under anaerobic conditions drastically enhanced the activity levels of the "reversible" but not of the "uptake" hydrogenase fraction. The "uptake" hydrogenase but not the "reversible" protein was activated by reduced thioredoxin. It is suggested that thioredoxin activates the H2-uptake by the membrane-bound "uptake" hydrogenase also in intact cells. The occurrence of the number of hydrogenases in cyanobacteria will be reevaluated.

Effects of tetrahydrocannabinol on rat preovulatory follicles: a quantitative cytochemical analysis

Using a microdensitometric histochemical assay, delta 5-3 beta-hydroxysteroid dehydrogenase activity and glucose-6-phosphate dehydrogenase Types I and II hydrogen generation were measured in preovulatory follicles from normal rats, and in follicles from rats given tetrahydrocannabinol for three days prior to sacrifice. Hydroxysteroid dehydrogenase and Type I hydrogen generation are involved in steroidogenesis, whereas Type II hydrogen generation is involved with general cellular metabolism. All ovaries were removed on pro-oestrus, frozen, sectioned and the sections reacted with the appropriate media. Enzyme activity was measured in the theca and in three regions of the membrana granulosa; peripheral, antral and corona radiata. Compared to control animals, the hydroxysteroid dehydrogenase activity was significantly reduced in all follicular regions in rats exposed to tetrahydrocannabinol. Type I hydrogen generation was significantly less in the theca and peripheral region of preovulatory follicles from rats given tetrahydrocannabinol, but the same in the antral region and corona radiata. In all follicular regions examined, Type II hydrogen generation was unchanged following tetrahydrocannabinol administration. Thus, only the enzymes specifically associated with follicular steroidogenesis were affected by administration of the drug.