Complementary use of the reversed-phase and anion-exchange modes of high-pressure liquid chromatography for studies of reduced nicotinamide adenine dinucleotide

UV-B- and oxidative stress-induced increase in nicotinamide and trigonelline and inhibition of defensive metabolism induction by poly(ADP-ribose)polymerase inhibitor in plant tissue

Nicotinamide and trigonelline contents increased in Catharanthus roseus tissue culture after exposure to 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH) or vanadylsulfate and in Pisum sativum leaves after exposure to UV-B radiation. Vanadylsulfate increased phenylalanine ammonia-lyase (PAL) activity and the content of reduced and oxidized gluthathione in C. roseus tissue culture. The increases in PAL activity caused by 2 mM AAPH or 0.2mM vanadylsulfate were prevented by 0.1 mM 3-aminobenzamide (3-AB), an inhibitor of poly(ADP-ribose)polymerase. Present results support the hypothesis [Berglund, T., FEBS Lett. (1994) 351, 145-149] that nicotinamide and/or its metabolites may function as signal transmittors in the response to oxidative stress in plants and that poly(ADP-ribose)polymerase has a function in the induction of defensive metabolism.

Characterization of the interaction of NADH with proton pumping E. coli transhydrogenase reconstituted in the absence and in the presence of bacteriorhodopsin

(1) Proton-pumping nicotinamide nucleotide transhydrogenase from Escherichia coli was purified in a reconstitutively active form employing affinity chromatography on immobilized palmitoyl-Coenzyme A. Reconstituted transhydrogenase showed an active proton pumping and a stimulation of the rate of reduction of 3-acetylpyridine-NAD+ by NADPH by uncouplers. Reconstitution in the absence of a thiol-reducing agent, e.g. dithiothreitol, abolished proton pumping without affecting catalytic activity, giving a decoupled transhydrogenase. (2) Co-reconstitution of transhydrogenase with bacteriorhodopsin gave vesicles which catalyzed a 5-10-fold increased rate of reduction of thio-NADP+ by NADH in the light. The Km for NADH, but not that for thio-NADP+, decreased markedly in the light, indicating an effect of the electrochemical proton potential on the affinity of the enzyme for NADH. Inhibition by substrate derivatives in the absence or presence of light supported this conclusion. Replacement of NADH with 2'-deoxy-NADH gave a strongly sigmoidal concentration dependence, indicating an allosteric change induced by binding to the NAD(H)-site. (3) Reduction of 3-acetylpyridine-NAD+ by NADH in the presence of NADPH, previously demonstrated to be catalyzed by both reconstituted bovine transhydrogenase and detergent-dispersed E. coli transhydrogenase, occurred at a pH below 6.5. This reaction did not pump protons. Proton pumping by 3-acetylpyridine-NAD+ plus NADPH occurred at a pH above 5.5. The two reactions were thus close to mutually exclusive, with a cross point at pH 5.8. Assuming a helix bundle structure of the membrane domain of transhydrogenase, a model is proposed involving histidine 91 of the beta subunit which previously was shown to be essential by site-directed mutagenesis. According to the model the extent of protonation of this histidine determines whether proton pumping or the NADH-3-acetylpyridine-NAD+ reaction takes place.

Analysis of pyridine dinucleotides in cultured rat hepatocytes by high-performance liquid chromatography

An isocratic reverse-phase high-performance liquid chromatography method for the separation and quantitation of total pyridine dinucleotides in hepatocyte cultures is described. Cells are extracted with cold 3 M perchloric acid or 0.5 N sodium hydroxide containing 50% (v/v) ethanol and 35% cesium chloride for the determination of the oxidized or reduced pyridine dinucleotides, respectively. Pyridine dinucleotides in the neutralized extracts were separated on an Excellopak ODS C18 (4.6 X 150 mm) column with 0.1 M potassium phosphate, pH 6.0, containing 3.75% methanol as the mobile phase. NAD+ and NADP+ were detected spectrophotometrically at 254 nm. The response was linear from 5 to 4000 pmol with recoveries of NAD+ and NADP+ of 98 and 101.1%, respectively. NADH and NADPH were monitored fluorometrically by activation at 370 nm and emission in the 400-700 nm range. The reduced pyridine dinucleotides had a linear response from 7.5 to 60 pmol with recoveries of NADH and NADPH of 99.4 and 101.3%, respectively. The coefficients of variation for all of the pyridine dinucleotide standards were less than 3.5%.

Determination of carbonyl groups in oxidatively modified proteins by reduction with tritiated sodium borohydride

Oxidatively modified proteins have been implicated in a variety of physiologic and pathologic processes. Oxidative modification typically causes inactivation of enzymes and also the introduction of carbonyl groups into amino acid side chains of the protein. We describe a method to quantify oxidatively modified proteins through reduction of these carbonyl groups with tritiated borohydride. The technique was applied to purified, oxidatively modified glutamine synthetase and to bronchoalveolar lavage fluid from dogs and from humans. Since the protein content of lung lavage fluid is low, a very sensitive method was required to measure the oxidized residues. Reduction of the carbonyl group generated during oxidation of proteins with tritiated borohydride provided excellent sensitivity. Incorporation of tritium was directly proportional to the amount of protein with a range from 10 to 1000 micrograms. Should moieties other than amino acids be labeled, they are easily removed by rapid benchtop hydrolysis of the protein followed by chromatography on Dowex 50.

Demonstration of the adenosine reservoirs with nitrobenzylthioinosine in liver and diaphragm by high-performance liquid chromatography

Purine nucleotides, nucleosides, nucleobases, dinucleotides and nucleosides derivatives from acid-extracted rat liver and diaphragm were separated and quantitated by reversed-phase ion-pair high-performance liquid chromatography with a mobile phase composed of 90 mM potassium phosphate, 15 mM tetrabutylammonium hydroxide and a 1-30% methanol gradient. During 5 min of ischemia, adenine and guanine nucleotides decreased along with significant declines in NAD and increases in adenosine, inosine, hypoxanthine, xanthine, NADP and adenylosuccinate. Nitrobenzylthioinosine by gavage (5 mg/kg per day for five days) increased adenosine levels but without any alteration in nucleobase levels. Adenosine was shuttled to every available intracellular reservoir which included in declining order of magnitude GDP greater than adenosylhomocysteine greater than adenosine greater than ADP greater than AMP greater than IMP = XMP = GMP.

Purification of bovine liver S-adenosylhomocysteine hydrolase by affinity chromatography on blue dextran-agarose

S-Adenosylhomocysteine (AdoHcy) hydrolase (adenosylhomocysteinase, EC 3.3.1.1) was purified from bovine liver by conventional protein purification procedures (differential centrifugation, ammonium sulfate fractionation and DEAE-cellulose chromatography) followed by affinity chromatography on blue dextran coupled to agarose. The enzyme was eluted from the blue dextran-agarose column with adenosine and the adenosine was removed by chromatography on Sephadex G-75. The affinity chromatography step resulted in a substantial increase in total AdoHcy hydrolase activity (about 600%) suggesting either removal of some inhibitory substance or a change in the structure of the protein producing a more catalytically efficient enzyme. The isolation procedure afforded over 3400-fold purification of the enzyme, which was shown to be homogeneous by polyacrylamide gel electrophoresis. Using high pressure liquid chromatography, the nucleotide content of the freshly purified enzyme was determined to be 2 mol of nicotinamide adenine nucleotide per mol of enzyme tetramer. The ratio of the reduced to the oxidized form of the nucleotide was correlated to the activity of the enzyme preparation.

Analysis of oxidized and reduced pyridine dinucleotides in rat liver by high-performance liquid chromatography

NADP+, NAD+, NADPH, and NADH were assayed by selective extraction and isocratic reversephase HPLC. Sample preparation involves freeze clamping and powdering liver under liquid nitrogen, extraction of dinucleotides with basic (reduced species) or acidic (oxidized species) cold ethanol, and injection onto the HPLC for quantitation at 340 nm (reduced) and 254 nm (oxidized). The mobile phase for the oxidized species is pH 5.25, 0.2 M ammonium phosphate/methanol, and for the reduced species is pH 6.0, 0.2 M ammonium phosphate/methanol/tributylamine. The method is linear over the range 0.016 to 2.0 nmol for the reduced species, and from 0.005 to 0.8 nmol for the oxidized pyridine dinucleotides. The recoveries were from 94.5% for NAD+ to 99.3% for NADPH, with standard deviations of approximately 2.5% for all species other than NADP+, which had a standard deviation of 10.4%. The coefficients of variation for repeated determinations of standards over 3 months were less than 4%.

S-Adenosylhomocysteine hydrolase from human placenta. Affinity purification and characterization

S-Adenosylhomocysteine hydrolase (EC 3.3.1.1) was purified to homogeneity from human placenta by using S-adenosylhomocysteine-agarose affinity chromatography. The enzyme is a tetramer with a native Mr of 189 000 and subunit Mr of 47 000-48 000; there were nine cysteine residues per subunit and no disulphide bonds. The pI was 5.7. H.p.l.c. analysis revealed that the enzyme contained four molecules of tightly bound cofactor (NAD) per tetramer, of which 10-50% was in the reduced form. The enzyme had four binding sites per tetramer for adenosine, of which 10-35% were found to be occupied. Two types of adenosine-binding sites could be distinguished on the basis of differences in rates of dissociation of the enzyme-adenosine complex, and by examining binding of adenosine at 0 degree C and 37 degrees C. The enzyme catalysed the interconversion of adenosine and 4',5'-dehydroadenosine; the equilibrium constant for this reaction was 2.1 and favoured 4',5'-dehydroadenosine formation. Variability in the specific activity of preparations of S-adenosylhomocysteine hydrolase was related to the NAD+/NADH ratio of the preparation. The capacity to bind radioactively labelled adenosine depended on the adenosine content of the purified enzyme. The rate of adenosine binding and the sensitivity of S-adenosylhomocysteine hydrolase to inactivation by adenosine were both diminished in the absence of dithiothreitol.

High-performance ion-exchange separation of oxidized and reduced nicotinamide adenine dinucleotides

High-performance anion-exchange chromatography of oxidized and reduced forms of nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) on a Pharmacia Mono Q anion-exchange column is reported. Microgram quantities of all four nucleotides can be separated at pH 7.7 in approximately 20 min. For preparative purposes, greater than 7 mg of NADH can be purified in a single injection, and the peak fractions have an A260 of greater than 80 OD units with an A260/A340 ratio of 2.25.