Energy conservation in Nitrobacter

Abstract The generation of ATP and NADH in total cells of Nitrobacter was measured under aerobic and anaerobic conditions. NADH synthesis was driven by an ATP independent reaction with nitrite or nitric oxide as electron donors. The rate of NADH formation was about 200 times higher, if nitric oxide instead of nitrite served as electron donor. Approximately 2 mol nitric oxide were needed for reduction of 1 mol NAD⁺. Nitrite caused an end-product inhibition of the nitric oxide induced NADH synthesis. ATP was synthesized by NADH oxidation with oxygen and nitrate as terminal electron acceptors.     

Reaction of the 2',3'-dialdehyde derivative of NADPH at a nucleotide site of bovine liver glutamate dehydrogenase

The 2',3'-dialdehyde derivative of NADPH (oNADPH) acts as a coenzyme for the reaction catalyzed by bovine liver glutamate dehydrogenase. Incubation of 250 microM oNADPH with enzyme for 300 min at 30 degrees C and pH 8.0 yields covalent incorporation of 1.0 mol of oNADPH/mol of enzyme subunit. The modified enzyme has a functional catalytic site and is activated by ADP, but is no longer inhibited by high NADH concentrations and exhibits decreased sensitivity to GTP inhibition. Using the change in inhibition by 600 microM NADH or 1 microM GTP to monitor the reaction leads to rate constants of 44.0 and 41.5 min-1 M-1, respectively, suggesting that loss of inhibition by the two regulatory compounds results from reaction by oNADPH at a single location. The oNADPH incorporation is proportional to the decreased inhibition by 600 microM NADH or 1 microM GTP, extrapolating to less than 1 mol of oNADPH/mol of subunit when the maximum change in NADH or GTP inhibition has occurred. Modified enzyme is still 93% inhibited at saturating levels of GTP, although its K1 is increased 20-fold to 4.6 microM. The kinetic effects caused by oNADPH are not prevented by alpha-ketoglutarate, ADP, 5 mM NADH, or 200 microM GTP alone, but are prevented by 5 mM NADH with 200 microM GTP. Incorporation of oNADPH into enzyme at 255 min is 0.94 mol/mol of peptide chain in the absence of ligands but only 0.53 mol/mol of peptide chain in the presence of the protectants 5 mM NADH plus 200 microM GTP. These results indicate that oNADPH modifies specifically about 0.4-0.5 sites/enzyme subunit or about 3 sites/enzyme hexamer and that reaction occurs at a GTP-dependent inhibitory NADH site of glutamate dehydrogenase.     

Inhibition by local anaesthetics of adenine nucleotide translocation in rat liver mitochondria

1. The mechanism of adenine nucleotide translocation in mitochondria isolated from rat liver was further examined by using the local anaesthetics procaine, butacaine, nupercaine and tetracaine as perturbators of lipid-protein interactions. Each of these compounds inhibited translocation of ADP and of ATP; butacaine was the most effective with 50% inhibition occurring at 30mum for 200mum-ATP and at 10mum for 200mum-ADP. The degree of inhibition by butacaine of both adenine nucleotides was dependent on the concentration of adenine nucleotide present; with low concentrations of adenine nucleotide, low concentrations of butacaine-stimulated translocation, but at high concentrations (greater than 50mum) low concentrations of butacaine inhibited translocation. Butacaine increased the affinity of the translocase for ATP to a value which approached that of ADP. 2. Higher concentrations of nupercaine and of tetracaine were required to inhibit translocation of both nucleotides; 50% inhibition of ATP translocation occurred at concentrations of 0.5mm and 0.8mm of these compounds respectively. The pattern of inhibition of ADP translocation by nupercaine and tetracaine was more complex than that of ATP; at very low concentrations (less than 250mum) inhibition ensued, followed by a return to almost original rates at 1mm. At higher concentrations inhibition of ADP translocation resulted. 3. That portion of ATP translocation stimulated by Ca(2+) was preferentially inhibited by each of the local anaesthetics tested. In contrast, inhibition by the anaesthetics of ADP translocation was prevented by low concentrations of Ca(2+). 4. The data provide further support for our hypothesis that lipid-protein interactions are important determinants in the activity of the adenine nucleotide translocase in mitochondria.     

Regulation of heart muscle pyruvate dehydrogenase kinase

1. The activity of pig heart pyruvate dehydrogenase kinase was assayed by the incorporation of [(32)P]phosphate from [gamma-(32)P]ATP into the dehydrogenase complex. There was a very close correlation between this incorporation and the loss of pyruvate dehydrogenase activity with all preparations studied. 2. Nucleoside triphosphates other than ATP (at 100mum) and cyclic 3':5'-nucleotides (at 10mum) had no significant effect on kinase activity. 3. The K(m) for thiamin pyrophosphate in the pyruvate dehydrogenase reaction was 0.76mum. Sodium pyrophosphate, adenylyl imidodiphosphate, ADP and GTP were competitive inhibitors against thiamin pyrophosphate in the dehydrogenase reaction. 4. The K(m) for ATP of the intrinsic kinase assayed in three preparations of pig heart pyruvate dehydrogenase was in the range 13.9-25.4mum. Inhibition by ADP and adenylyl imidodiphosphate was predominantly competitive, but there was nevertheless a definite non-competitive element. Thiamin pyrophosphate and sodium pyrophosphate were uncompetitive inhibitors against ATP. It is suggested that ADP and adenylyl imidodiphosphate inhibit the kinase mainly by binding to the ATP site and that the adenosine moiety may be involved in this binding. It is suggested that thiamin pyrophosphate, sodium pyrophosphate, adenylyl imidodiphosphate and ADP may inhibit the kinase by binding through pyrophosphate or imidodiphosphate moieties at some site other than the ATP site. It is not known whether this is the coenzyme-binding site in the pyruvate dehydrogenase reaction. 5. The K(m) for pyruvate in the pyruvate dehydrogenase reaction was 35.5mum. 2-Oxobutyrate and 3-hydroxypyruvate but not glyoxylate were also substrates; all three compounds inhibited pyruvate oxidation. 6. In preparations of pig heart pyruvate dehydrogenase free of thiamin pyrophosphate, pyruvate inhibited the kinase reaction at all concentrations in the range 25-500mum. The inhibition was uncompetitive. In the presence of thiamin pyrophosphate (endogenous or added at 2 or 10mum) the kinase activity was enhanced by low concentrations of pyruvate (25-100mum) and inhibited by a high concentration (500mum). Activation of the kinase reaction was not seen when sodium pyrophosphate was substituted for thiamin pyrophosphate. 7. Under the conditions of the kinase assay, pig heart pyruvate dehydrogenase forms (14)CO(2) from [1-(14)C]pyruvate in the presence of thiamin pyrophosphate. Previous work suggests that the products may include acetoin. Acetoin activated the kinase reaction in the presence of thiamin pyrophosphate but not with sodium pyrophosphate. It is suggested that acetoin formation may contribute to activation of the kinase reaction by low pyruvate concentrations in the presence of thiamin pyrophosphate. 8. Pyruvate effected the conversion of pyruvate dehydrogenase phosphate into pyruvate dehydrogenase in rat heart mitochondria incubated with 5mm-2-oxoglutarate and 0.5mm-l-malate as respiratory substrates. It is suggested that this effect of pyruvate is due to inhibition of the pyruvate dehydrogenase kinase reaction in the mitochondrion. 9. Pyruvate dehydrogenase kinase activity was inhibited by high concentrations of Mg(2+) (15mm) and by Ca(2+) (10nm-10mum) at low Mg(2+) (0.15mm) but not at high Mg(2+) (15mm).     

Kinetic properties of a magnesium ion- and calcium ion-stimulated adenosine triphosphatase from the outer-membrane fraction of rat spleen mitochondria

1. Isolated outer membranes from rat spleen mitochondria can be stored in liquid N(2) for several weeks without significant loss of ATPase (adenosine triphosphatase) activity. 2. The ATPase reaction has a broad pH optimum centering on neutral pH, with little significant activity above pH9.0 or below pH5.5. 3. A sigmoidal response of the ATPase activity to temperature is observed between 0 and 55 degrees C, with complete inactivation at 60 degrees C. The Arrhenius plot shows that the activation energy above the transition temperature (22 degrees C) (E(a)=144kJ/mol) is one-third of that calculated for below the transition temperature (E'(a)=408kJ/mol). 4. The outer-membrane ATPase (K(m) for MgATP=50mum) is inactive unless Mg(2+) is added, whereas the inner-membrane ATPase (K(m) for ATP=11mum) is active without added Mg(2+) unless the mitochondria have been depleted of all endogenous Mg(2+) (by using ionophore A23187). 5. The substrate for the outer-membrane ATPase is a bivalent metal ion-nucleoside triphosphate complex in which Mg(2+) (K(m)=50mum) can be replaced effectively by Ca(2+) (K(m)=6.7mum) or Mn(2+), and ATP by ITP. Cu(2+), Co(2+), Sr(2+), Ba(2+), Ni(2+), Cd(2+) and Zn(2+) support very little ATP hydrolysis. 6. Univalent metal ions (Na(+), K(+), Rb(+), Cs(+) and NH(4) (+), but not Li(+)) stimulate the MgATPase activity (<10%) at low concentrations (50mm), but, except for K(+), are slightly inhibitory (20-30%) at higher concentrations (500mm). 7. The Mg(2+)-stimulated ATPase activity is significantly inhibited by Cu(2+) (K(i)=90mum), Ni(2+) (K(i)=510mum), Zn(2+) (K(i)=680mum) and Co(2+) (K(i)=1020mum), but not by Mg(2+), Ca(2+), Ba(2+) or Sr(2+). 8. The outer-membrane ATPase is insensitive to the inhibitors oligomycin, NN'-dicyclohexylcarbodiimide, NaN(3), ouabain and thiol-specific reagents. A significant inhibition is observed at high concentrations of AgNO(3) (0.5mm) and NaF (10mm). 9. The activity towards MgATP is competitively inhibited by the product MgADP (K(i)=0.7mm) but not by the second product P(i) or by 5'-AMP.     

Reversal of oxidative phosphorylation in submitochondrial particles using glucose 6-phosphate and hexokinase as an ATP regenerating system.

During steady-state, the Pi released in the medium is derived from glucose-6-phosphate which continuously regenerates the ATP hydrolyzed. A membrane potential (delta psi) can be built up in submitochondrial particles using glucose-6-phosphate and hexokinase as an ATP-regenerating system. The energy derived from the membrane potential thus formed, can be used to promote the energy-dependent transhydrogenation from NADH to NADP+ and the uphill electron transfer from succinate to NAD+. In spite of the large differences in the energies of hydrolysis of ATP (delta G degrees = -7.0 to -9.0 kcal/mol) and of glucose-6-phosphate (delta G degrees = -2.5 kcal/mol), the same ratio between Pi production and either NADPH or NADH formation were measured regardless of whether millimolar concentrations of ATP or a mixture of ADP, glucose-6-phosphate and hexokinase were used. Rat liver mitochondria were able to accumulate Ca2+ when incubated in a medium containing hexokinase, ADP and glucose-6-phosphate. The different reaction measured with the use of glucose-6-phosphate and hexokinase were inhibited by glucose concentrations varying from 0.2 to 2 mM. Glucose shifts the equilibrium of the reaction towards glucose-6-phosphate formation thus leading to a decrease of the ATP concentration in the medium.     

Affinity labeling of an allosteric ADP site of glutamate dehydrogenase by 2-(4-bromo-2,3-dioxobutylthio)adenosine 5'-monophosphate

Bovine liver glutamate dehydrogenase reacts covalently with the adenine nucleotide analogue 2-(4-bromo-2,3-dioxobutylthio)adenosine 5'-monophosphate (2-BDB-TAMP) with incorporation of about 1 mol of reagent/mol of enzyme subunit. The modified enzyme is not inactivated by this reaction as measured in the absence of allosteric effectors. Native glutamate dehydrogenase is activated by ADP and inhibited by high concentrations of NADH; both of these effects are irreversibly decreased upon reaction of the enzyme with 2-BDB-TAMP. The decrease in activation by ADP was used to determine the rate constant for reaction with 2-BDB-TAMP. The rate constant (kobs) for loss of ADP activation exhibits a nonlinear dependence on 2-BDB-TAMP concentration, suggesting a reversible binding of reagent (KR = 0.74 mM) prior to irreversible modification. At 1.2 mM 2-BDB-TAMP, kobs = 0.060 min-1 and is not affected by alpha-ketoglutarate or GTP, but is decreased to 0.020 min-1 by 5 mM NADH and to zero by 5 mM ADP. Incorporation after incubation with 1.2 mM 2-BDB-TAMP for 1 h at pH 7.1 is 1.02 mol/mol enzyme subunit in the absence but only 0.09 mol/subunit in the presence of ADP. The enzyme protected with 5 mM ADP behaves like native enzyme in its activation by ADP and in its inhibition by NADH. Native enzyme binds reversibly 2 mol of [14C]ADP/subunit, whereas modified enzyme binds only 1 mol of ADP/peptide chain. These results indicate that incorporation of 1 mol of 2-BDB-TAMP causes elimination of one of the ADP sites of the native enzyme. 2-BDB-TAMP acts as an affinity label of an ADP site of glutamate dehydrogenase and indirectly influences the NADH inhibitory site.     

The molecular weight and thiol residues of acetyl-coenzyme A synthetase from ox heart mitochondria

1. A constant molecular weight of 57000 was obtained by gel filtration of highly purified acetyl-CoA synthetase over a 1000-fold range of enzyme concentrations. The amino acid analysis is reported. 2. With native enzyme at 20 degrees C the relatively rapid reaction of four thiol residues with p-hydroxymercuribenzoate caused an immediate inhibition reversible by either CoA or mercaptoethanol. Other substrates did not protect against this rapid inhibition. 3. The much slower reaction of the remaining four thiol residues was independent of the concentration of the mercurial, first-order with respect to enzyme, and had a large energy of activation (+136kJ/mol), suggesting that a conformation change in the protein was rate-limiting. This slow phase of the reaction was accompanied by an irreversible inactivation of the enzyme. 4. The effects of substrates on this irreversible inactivation at pH7.0 in 5 mm-MgCl(2) indicated strong binding of ATP and pyrophosphate by the enzyme (concentrations for half-maximal effects, K((1/2)), were <30mum and <10mum respectively) and weaker binding of acetyl-CoA (K((1/2)) about 1 mm), AMP (K((1/2)) about 2mm) and acetate. In the presence of acetate, MgCl(2) and p-hydroxymercuribenzoate, titration of the enzyme with ATP revealed at least two ATP binding sites/mol. 5. The experiments suggest that reaction of the thiol residues with mercurial causes loss of enzymic activity by altering the structure of the enzyme, rather than that the thiol residues play a direct role in the catalysis.     

Inhibition of purine phosphoribosyltransferases from Ehrlich ascites-tumour cells by purine nucleotides

1. The purine bases adenine, hypoxanthine and guanine were rapidly incorporated into the nucleotide fraction of Ehrlich ascites-tumour cells in vivo. 2. The reaction of 5'-phosphoribosyl pyrophosphate with adenine phosphoribosyltransferase from ascites-tumour cells (K(m) 6.5-11.9mum) was competitively inhibited by AMP, ADP, ATP and GMP (K(i) 7.5, 21.9, 395 and 118mum respectively). Similarly the reactions of 5'-phosphoribosyl pyrophosphate with both hypoxanthine phosphoribosyltransferase and guanine phosphoribosyltransferase (K(m) 18.4-31 and 37.6-44.2mum respectively) were competitively inhibited by IMP (K(i) 52 and 63.5mum) and by GMP (K(i) 36.5 and 5.9mum). 3. The nucleotides tested as inhibitors did not appreciably compete with the purine bases in the phosphoribosyltransferase reactions. 4. It was postulated that the purine phosphoribosyltransferases of Ehrlich ascites-tumour cells may be effectively separated from the adenine nucleotide pool of these cells.     

Phosphorylation and the Reduced Nicotinamide Adenine Dinucleotide Oxidase Reaction in Streptococcus agalactiae

Cell-free extracts from aerobically grown Streptococcus agalactiae cells possess a reduced nicotinamide adenine dinucleotide (NADH) oxidase which is linked to oxygen. It is inhibited by cyanide, although cytochromes evidently are not involved. Adenosine triphosphate (ATP) formation occurs during the reaction, but 66 to 75% of the total ATP is formed nonoxidatively. The remaining 25 to 35% of the ATP formation is related to the oxidation of NADH. The formation of ATP in the oxidative reaction can be prevented by excluding oxygen or adding cyanide to prevent NADH oxidation. It can also be prevented by adding methylene blue or pyruvate, which bypasses electron transport to oxygen, but does not interfere with NADH oxidation. Potential sources of ATP, such as glycolysis, the pyruvate oxidase reaction, or the oxidative pentose cycle, are not present, and the high nonoxidative ATP formation is ascribed to the adenylate kinase reaction. The reaction requires adenosine diphosphate (ADP) as a phosphate acceptor. NADH oxidation is independent of ADP. Antimycin A, amytal, and 2,4-dinitrophenol decreased, but did not prevent, oxidative formation of ATP. P:O ratios ranged from 0.15 to 0.25. All of the oxidative activity was in the soluble portion of the cell-free extracts.     

Monodehydroascorbate reductase from cucumber is a flavin adenine dinucleotide enzyme

Monodehydroascorbate reductase (EC 1.6.5.4) was purified from cucumber fruit to a homogeneous state as judged by polyacrylamide gel electrophoresis. The cucumber monodehydroascorbate reductase was a monomer with a molecular weight of 47,000. It contained 1 mol of FAD/mol of enzyme which was reduced by NAD(P)H and reoxidized by monodehydroascorbate. The enzyme had an exposed thiol group whose blockage with thiol reagents inhibited the electron transfer from NAD(P)H to the enzyme FAD. Both NADH and NADPH served as electron donors with Km values of 4.6 and 23 microM, respectively, and Vmax of 200 mol of NADH and 150 mol of NADPH oxidized mol of enzyme-1 s-1. The Km for monodehydroascorbate was 1.4 microM. The amino acid composition of the enzyme is presented. In addition to monodehydroascorbate, the enzyme catalyzed the reduction of ferricyanide and 2,6-dichloroindophenol but showed little reactivity with calf liver cytochrome b5 and horse heart cytochrome c. The kinetic data suggested a ping-pong mechanism for the monodehydroascorbate reductase-catalyzed reaction. Cucumber monodehydroascorbate reductase occurs in soluble form and can be distinguished from NADPH dehydrogenase, NADH dehydrogenase, DT diaphorase, microsome-bound NADH-cytochrome b5 reductase, and NADPH-cytochrome c reductase by its molecular weight, amino acid composition, and specificity of electron acceptors and donors.     

The regulation of poly-β-hydroxybutyrate metabolism in Azotobacter beijerinckii

1. The enzymes beta-ketothiolase, acetoacetyl-CoA reductase, acetoacetate-succinate CoA-transferase (;thiophorase') and d(-)-3-hydroxybutyrate dehydrogenase have been partially purified from crude extracts of glucose-grown nitrogen-fixing batch cultures of Azotobacter beijerinckii. The condensation of acetyl-CoA to acetoacetyl-CoA catalysed by beta-ketothiolase is inhibited by CoASH, and the reverse reaction is inhibited by acetoacetyl-CoA. Acetoacetyl-CoA reductase has K(m) for acetoacetyl-CoA of 1.8mum and is inhibited by acetoacetyl-CoA above 10mum. The enzyme utilizes either NADH or NADPH as electron donor. The second enzyme of poly-beta-hydroxybutyrate degradation, d(-)-3-hydroxybutyrate dehydrogenase, is NAD(+)-specific and is inhibited by NADH, pyruvate and alpha-oxoglutarate. CoA transferase is inhibited by acetoacetate, the product of hydroxybutyrate oxidation. In continuous cultures poly-beta-hydroxybutyrate biosynthesis ceased on relaxation of oxygen-limitation and the rates in situ of oxygen consumption and carbon dioxide evolution of such cultures increased without a concomitant increase in glucose uptake. 2. On the basis of these and other findings a cyclic mechanism for the biosynthesis and degradation of poly-beta-hydroxybutyrate is proposed, together with a regulatory scheme suggesting that poly-beta-hydroxybutyrate metabolism is controlled by the redox state of the cell and the availability of CoASH, pyruvate and alpha-oxoglutarate. beta-Ketothiolase plays a key role in the regulatory process. Similarities to the pathways of poly-beta-hydroxybutyrate biosynthesis and degradation in Hydrogenomonas are discussed.     

A soluble NADH dehydrogenase (NADH: ferricyanide oxidoreductase) from Thermus aquaticus strain T351.

A soluble NADH dehydrogenase (NADH:ferricyanide oxidoreductase) has been obtained by simple disruption of cells of Thermus aquaticus strain T351, and purified. The enzyme is of low molecular mass, 50 000 Da, and displays many of the properties of the membrane-bound enzyme, including inhibition by both NADH and ferricyanide, and the same Km for ferricyanide. The enzyme contains 0.05 mol of FMN, 0.16 mol of labile sulphur and 2.2 mol of iron per mol of protein. The enzyme is inhibited by NAD and cupferron competitively with ferricyanide, and by ATP (but not ADP) competitively with NADH. The enzyme is particularly thermostable, having a half-life at 95 degrees C of 35 min. The effect of temperature on the molar absorption coefficient and the stability of NADH was determined.     

Myeloperoxidase potentiates nitric oxide-mediated nitrosation

Nitrosation is an important reaction elicited by nitric oxide (NO). To better understand how nitrosation occurs in biological systems, we assessed the effect of myeloperoxidase (MPO), a mediator of inflammation, on nitrosation observed during NO autoxidation. Nitrosation of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ; 10 mum) to 2-nitrosoamino-3-methylimidazo[4,5-f]quinoline (N-NO-IQ) was monitored by HPLC. Using the NO donor spermine NONOate at pH 7.4, MPO potentiated N-NO-IQ formation. The minimum effective quantity of necessary components was 8.5 nm MPO, 0.25 mum H(2)O(2)/min, and 0.024 mum NO/min. Autoxidation was only detected at >/=1.2 mum NO/min. MPO potentiation was not affected by a 40-fold excess flux of H(2)O(2) over NO or less than a 2.4-fold excess flux of NO over H(2)O(2). Potentiation was due to an 8.8-fold increased affinity of MPO-derived nitrosating species for IQ. Autoxidation was inhibited by azide, suggesting involvement of the nitrosonium ion, NO(+). MPO potentiation was inhibited by NADH, but not azide, suggesting oxidative nitrosylation with NO(2)(.) or an NO(2)(.)-like species. MPO nonnitrosative oxidation of IQ with 0.3 mm NO(2)(-) at pH 5.5 was inhibited by azide, but not NADH, demonstrating differences between MPO oxidation of IQ with NO compared with NO(2)(-). Using phorbol ester-stimulated human neutrophils, N-NO-IQ formation was increased with superoxide dismutase and inhibited by catalase and NADH, but not NaN(3). This is consistent with nitrosation potentiation by MPO, not peroxynitrite. Increased N-NO-IQ formation was not detected with polymorphonuclear neutrophils from two unrelated MPO-deficient patients. Results suggest that the highly diffusible stable gas NO could initiate nitrosation at sites of neutrophil infiltration.     

Fate of nucleotides bound to reconstituted Fo-F1 during adenosine 5'-triphosphate synthesis activation or hydrolysis: role of protein inhibitor and hysteretic inhibition

The protein ATPase inhibitor entraps about five nucleotides in pig heart mitochondrial F1, one at least being a triphosphate [Di Pietro, A., Penin, F., Julliard, J.H., Godinot, C., & Gautheron, D.C. (1988) Biochem. Biophys. Res. Commun. 152, 1319-1325]. The fate of these nucleotides was studied during ATP synthesis driven by NADH oxidation in reconstituted inverted submitochondrial particles. Iodinated F1, containing 0.7 mol of endogenous nucleotides/mol, was first loaded with tritiated adenine nucleotides in the presence or absence of the protein inhibitor and then reassociated with F1-depleted submitochondrial particles (ASU particles) to reconstitute an efficient NADH-driven ATP synthesis. In the absence of the protein inhibitor, 1.7 mol of labeled nucleotides remained bound per mole of reassociated F1, 0.8-0.9 mol being rapidly exchangeable against medium ADP or ATP, as measured after rapid filtration through nitrocellulose filters. In the presence of the protein inhibitor, as many as 3.25 mol of labeled nucleotides remained bound per mole of reassociated F1. Under hydrolysis conditions where ATPase activity was highly inhibited, no release of tritiated nucleotide occurred. In contrast, under ATP synthesis conditions where the protonmotive force was generated by NADH oxidation, the progressive reversal of inhibition by the protein inhibitor was correlated to a concomitant release of tritiated nucleotide. When ATP synthesis became fully active, about one nucleotide was completely exchanged whereas more than three nucleotides remained tightly bound and did not appear to be directly involved in ATP synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Photophosphorylation and oxidative phosphorylation in intact cells and chromatophores of an aerobic photosynthetic bacterium, Erythrobacter sp. strain OCh114.

Light-induced ATP synthesis was studied in intact cells and chromatophores of Erythrobacter sp. strain OCh114. ATP synthesis was measured by both the pH method and the luciferin-luciferase luminescence method. The rate of ATP synthesis was moderate (a typical value of 0.65 mol of ATP per mol of bacteriochlorophyll per min), and synthesis was inhibited by antimycin A. ATP was synthesized under illumination only under aerobic conditions and not under anaerobic conditions. This characteristic was similar to that of other light-induced energy transduction processes in this bacterial species, such as oxidation of reaction center, oxidation of cytochrome c551, and translocation of H+, which were not observed under anaerobic conditions. This phenomenon was reconciled with the fact that the Erythrobacter sp. could not grow anaerobically even in the light. The characteristics of oxidative phosphorylation and ATP hydrolysis were also investigated. The respiratory ratio of chromatophores was 2.3. Typical rates of oxidative phosphorylation by NADH and by succinate were 2.9 mol of ATP per mol of bacteriochlorophyll per min (P/O = 0.22) and 1.1 mol of ATP per mol of bacteriochlorophyll per min (P/O = 0.19), respectively. A typical rate of ATP hydrolysis was 0.25 mol of ATP per mol of bacteriochlorophyll per min in chromatophores. ATPase and adenylate kinase are also involved in the metabolism of adenine nucleotides in this bacterium.     

Studies on energy-linked reactions. Energy-linked reduction of oxidized nicotinamide–adenine dinucleotide by succinate in Escherichia coli

1. A method for the preparation of small particles from Escherichia coli is described. 2. These particles catalyse the ATP-driven reduction of NAD⁺ by succinate. 3. ATP utilized/NADH produced ratios below 2.0 were measured and a stoicheiometry of 1 molecule of ATP utilized per molecule of NADH produced is proposed. 4. The reaction is not inhibited by 2,4-dinitrophenol or by oligomycin but is inhibited by other uncouplers such as pentabromophenol and dicoumarol. 5. The specificity of the energy source, the specificity of the electron acceptor, the effects of pH, Mg²⁺, P_i and temperature have been studied.     

Affinity labeling of bovine liver glutamate dehydrogenase with 8-[(4-bromo-2,3-dioxobutyl)thio]adenosine 5'-diphosphate and 5'-triphosphate

Bovine liver glutamate dehydrogenase reacts with 8-[(4-bromo-2,3-dioxobutyl)thio]adenosine 5'-diphosphate (8-BDB-TA-5'-DP) and 5'-triphosphate (8-BDB-TA-5'-TP) to yield enzyme with about 1 mol of reagent incorporated/mol of enzyme subunit. The modified enzyme is catalytically active but has decreased sensitivity to inhibition by GTP, reduced extent of activation by ADP, and diminished inhibition by high concentrations of NADH. Since modified enzyme, like native glutamate dehydrogenase, reversibly binds more than 1 mol each of ADP and GTP, it is unlikely that 8-BDB-TA-5'-TP reacts directly within either the ADP or GTP regulatory sites. The rate constant for reaction of enzyme exhibits a nonlinear dependence on reagent concentration with KD = 89 microM for 8-BDB-TA-5'-TP and 240 microM for 8-BDB-TA-5'-DP. The ligands ADP and GTP alone and NADH alone produce only small decreases in the rate constant for the reaction of enzyme with 8-BDB-TA-5'-TP, but the combined addition of 5 mM NADH + 200 microM GTP reduces the reaction rate constant more than 10-fold and the reagent incorporation to about 0.1 mol/mol of enzyme subunit. These results suggest that 8-BDB-TA-5'-TP reacts as a nucleotide affinity label in the region of the GTP-dependent NADH regulatory site of bovine liver glutamate dehydrogenase.     

Chemiluminescent assay of co-factors

Bioluminescent methods are widely used for the assay of the co-factors, NADH and ATP. Although the bioluminescent method is highly sensitive, the enzymes used are unstable and expensive. Therefore a chemiluminescent method would be valuable in clinical routine assay. We have developed a chemiluminescent method for the assay of NADH using the 1-methoxy-5-methylphenazinium methyl sulphate (1-MPMS)/isoluminol(IL)/microperox-idase(m-POD) system. In order to increase the sensitivity of this method, enzymatic cycling system was coupled to the chemiluminescent assay of NADH. Alcohol dehydrogenase and malate dehydrogenase were used as the cycling enzyme. The standard curve was obtained in the range from 3 × 10^?14 to 5 × 10^?12mol/assay. The detection limit of NADH was 30fmol/assay which was comparable to that of the bioluminescent method using bacterial luciferase. Two chemiluminescent methods for the assay of ATP have been developed. Method 1 is the system using hexokinase/G6PDH and 1-PMS/IL/m-POD, and method 2 is the system based on the enzymatic cycling reaction of ATP using hexokinase/pyruvate kinase. Method 2 is 1000/fold more sensitive than the method 1. The detection limit of ATP was 10 fmol/assay.     

A chromophoric and fluorescent analog of GTP, 2',3'-O-(2,4,6-trinitrocyclohexadienylidene)-GTP, as a spectroscopic probe for the GTP inhibitory site of liver glutamate dehydrogenase

The ribose-modified chromophoric and fluorescent analog of ATP, 2',3'-O-(2,4,6-trinitrocyclohexadienylidene)-ATP (TNP-ATP) (Hiratsuka, T., and Uchida, K. (1973) Biochim. Biophys. Acta 320, 635-647 and Hiratsuka, T. (1976) Biochim. Biophys. Acta 453, 293-297) has been widely used as an ATP analog for various ATPases. Although the corresponding analog of GTP,2',3'-O-(2,4,6-trinitrocyclohexadienylidene)-GTP (TNP-GTP) should be useful for the study of various GTP-requiring enzymes, it is difficult to prepare TNP-GTP by the conventional method. In the present study, we succeeded in the synthesis of TNP-GTP with the use of an alternative method. The analogs of GDP, GMP, and guanyl-5'-yl imidodiphosphate (Gpp(NH)p) were also synthesized. Visible absorption and fluorescent properties of TNP-GTP, TNP-GDP, TNP-GMP, and TNP-Gpp(NH)p were quite similar to those of TNP-ATP. TNP-GTP was found to be able to replace GTP as an inhibitor for bovine liver glutamate dehydrogenase. The enzyme was inhibited by TNP-GTP to a maximum extent of 54% at saturating concentrations of the analog with a KI of 2.7 microM. TNP-Gpp(NH)p and other ribose-modified fluorescent analogs of GTP,3'-O-anthraniloyl-GTP and 3'-O-(N-methylanthraniloyl)-GTP (Hiratsuka, T. (1983) Biochim. Biophys. Acta 742, 496-508), also inhibited the enzymatic activity. Binding of TNP-GTP to the enzyme was characterized by a 5.6-fold enhancement in analog fluorescence. In the presence of NADH, the limiting fluorescence enhancement of the bound analog decreased to 2.7-fold. As determined by fluorometric titration, the maximum number of TNP-GTP binding sites on the enzyme was 1.9 mol/mol of subunit with a KD of 0.66 microM in the absence of NADH and 2.2 mol/mol of subunit with two KD values of 0.11 and 0.71 microM in the presence of NADH. These observations suggest that NADH binding increases the affinity of only 1 mol of the 2 mol of TNP-GTP bound to the enzyme. These spectroscopic and biological properties of TNP-GTP should make this analog useful as a chromophoric and fluorescent probe for studies not only of glutamate dehydrogenase but also of various GTP-requiring enzymes, which have a high specificity for the base moiety of GTP.