Chemo-enzymatic synthesis of a bioactive peptide containing a glutamine-linked oligosaccharide and its characterization

A bioactive peptide containing a glutamine-linked oligosaccharide was chemo-enzymatically synthesized by use of the solid-phase method of peptide synthesis and the transglycosylation activity of endo-β-N-acetylglucosaminidase. Substance P, a neuropeptide, is an undecapeptide containing two l-glutamine residues. A substance P derivative with an N-acetyl-d-glucosamine residue attached to the fifth or sixth l-glutamine residue from the N-terminal region was chemically synthesized. A sialo complex-type oligosaccharide derived from a glycopeptide of hen egg yolk was added to the N-acetyl-d-glucosamine moiety of the substance P derivative using the transglycosylation activity of endo-β-N-acetylglucosaminidase from Mucor hiemalis, and a substance P derivative with a sialo complex-type oligosaccharide attached to the l-glutamine residue was synthesized. This glycosylated substance P was biologically active, although the activity was rather low, and stable against peptidase digestion. The oligosaccharide moiety attached to the l-glutamine residue of the peptide was not liberated by peptide-N⁴-(N-acetyl-β-d-glucosaminyl) asparagine amidase F.     

Cooperative interaction of reduced pyridine nucleotides with estrogen synthetase of human placental microsomes

The estrogen synthetase present in human placental microsomes appears to be dependent on the cooperative interaction of the reduced cofactors NADPH and NADH for optimal activity. Using steady-state concentrations of either cofactor, it was found that while the estrogen synthetase activity followed hyperbolic saturation kinetics with NADPH (K_mapp = 14 μM), the enzyme followed sigmoidal saturation kinetics when the cofactor was NADH, with the half-maximum velocity attained at a cofactor concentration of 1.1 mm. The maximum velocity obtained with NADPH as the cofactor was greater than with corresponding concentrations of NADH. Estrogen synthetase activity in the presence of NADH was not due to NADPH contamination. NADH, in the presence of small concentrations of NADPH (0.5 to 5 μm), stimulated significantly the rate of estrogen formation from androstenedione by placental microsomes and, in addition, the enzyme saturation kinetics changed from sigmoidal to hyperbolic, thus mimicking the effect of NADPH. Estrogen synthetase activity, measured in the presence of 1 mm NADH, was stimulated in a dose-dependent manner by NADPH (K_mapp = 0.4 μM NADPH) and, when the enzyme was measured in the presence of 5 μm NADPH, the activity was stimulated in a dose-dependent manner by NADH (K_mapp = 45 μM NADH). Estrogen synthetase activity measured in the presence of NADH, without and with NADPH (1 μm) remained linear both with time of incubation for approximately 15 min and with microsomal protein concentration up to 3 mg/ml. The apparent K_m of estrogen synthetase for androstenedione, when measured in the presence of NADH, was 1 μm. The synergistic interaction between NADH and NADPH in stimulating placental estrogen synthetase activity observed in vitro may, conceivably, take place in vivo in the intact placenta.     

Formation of γ-glutamylglycyglycine by extracellular glutaminase of Aspergillus oryzae

γ-Glutamylglycylglycine (γ-GluGlyGly) was formed through the γ-glutamyltranspeptidase (GGT) reaction catalyzed by glutaminase in a water extract of wheat bran koji obtained with Aspergillus oryzae MA-27-IM. The yield of γ-GluGlyGly was about 18% from l-glutamine in a reaction mixture containing 50 mM l-glutamine, 50 mM glycylglycine, and the extract (0.1 unit ml as GGT activity) in a 100 mM Tris-HCl buffer solution (pH 7.2), which was incubated for 7 h at 30°C. The γ-GluGlyGly formed was purified by ion exchange chromatographies, and the identified by chemical and enzymatic methods as well as by infrared and PMR spectroscopic analyses.     

Respective role of superoxide and hydroxyl radical in the activity of the reconstituted microsomal ethanol-oxidizing system.

Superoxide dismutase, a scavenger of O^?₂. does not affect the rate of ethanol oxidation in a reconstituted system containing purified cytochrome P-450, NADPH-cytochrome c reductase, and dilauroyl l-3-phosphatidyl choline. The same concentration of Superoxide dismutase (50 μg/ml) completely abolishes the oxidation of epinephrine in this reconstituted system and ethanol oxidation by the xanthine-xanthine oxidase. Ethanol is not oxidized by the reconstituted system when NADPH is replaced by H₂O₂ but the addition of H₂O₂ to this sytem containing NADPH accelerates ethanol oxidation. This increase is abolished by the addition of Superoxide dismutase. Hydroxyl radical scavengers (50 mm dimethylsulfoxide, 100 mm benzoate, 100 mm mannitol, 20 mm thiourea) diminish the oxidation of ethanol in the reconstituted system by 48 to 76%. Thus hydroxyl radical may participate in the activity of reconstituted ethanol-oxidizing system, whereas Superoxide is not involved.     

Structural and thermodynamic insights into the assembly of the heteromeric pyridoxal phosphate synthase from Plasmodium falciparum

Pyridoxal 5′-phosphate (PLP) is required as a cofactor by many enzymes. The predominant de novo biosynthetic route is catalyzed by a heteromeric glutamine amidotransferase consisting of the synthase subunit Pdx1 and the glutaminase subunit Pdx2. Previously, Bacillus subtilis PLP synthase was studied by X-ray crystallography and complex assembly had been characterized by isothermal titration calorimetry. The fully assembled PLP synthase complex contains 12 individual Pdx1/Pdx2 glutamine amidotransferase heterodimers. These studies revealed the occurrence of an encounter complex that is tightened in the Michaelis complex when the substrate l-glutamine binds. In this study, we have characterized complex formation of PLP synthase from the malaria-causing human pathogen Plasmodium falciparum using isothermal titration calorimetry. The presence of l-glutamine increases the tightness of the interaction about 30-fold and alters the thermodynamic signature of complex formation. The thermodynamic data are integrated in a 3D homology model of P. falciparum PLP synthase. The negative experimental heat capacity (C_p) describes a protein interface that is dominated by hydrophobic interactions. In the absence of l-glutamine, the experimental C_p is less negative than in its presence, contrasting to the previously characterised bacterial PLP synthase. Thus, while the encounter complexes differ, the Michaelis complexes of plasmodial and bacterial systems have similar characteristics concerning the relative contribution of apolar/polar surface area. In addition, we have verified the role of the N-terminal region of PfPdx1 for complex formation. A “swap mutant” in which the complete αN-helix of plasmodial Pdx1 was exchanged with the corresponding segment from B. subtilis shows cross-binding to B. subtilis Pdx2. The swap mutant also partially elicits glutaminase activity in BsPdx2, demonstrating that formation of the protein complex interface via αN and catalytic activation of the glutaminase are linked processes.     

Some properties of purified 3-hydroxy-3-methylglutaryl coenzyme A reductase phosphatases from rat liver

Incubation of four purified rat liver 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase phosphatases (G. Gil, M. Sitges, and F. G. Hegardt, (1981) Biochim. Biophys. Acta663, 211–221) with HMG-CoA, CoA, NADPH, or citrate caused a concentration-dependent inactivation of the enzyme activities. HMG-CoA and CoA showed similar patterns of inactivation and at 0.5 mm of both compounds, the four reductase phosphatases were fully inhibited. Half-maximal inactivation was comprised between 0.02 and 0.1 mm of HMG-CoA and CoA. NADPH at concentration ranging between 5 and 10 mm produced complete inactivation of reductase phosphatases. Citrate at 5 mm produced full inactivation, and half-maximal inhibition ranged from 0.1 to 0.4 mm for the different phosphatases. The behavior of fluoride varied with respect to the four phosphatases: Low molecular forms were inactivated in a similar manner as described for other protein phosphatases. However, high molecular forms were slightly inactivated, and phosphatase IIa at 100 mm showed a level of activity similar to the control. The effect of KCl on the four reductase phosphatases could explain this behavior since at high concentrations, KCl (and NaCl) produced activation in both high and low molecular forms, this effect being more enhanced in high M_r reductase phosphatases. The insensitivity to fluoride of high M_r reductase phosphatases could explain the discrepancies in percentage of the active form of HMG-CoA reductase described previously in literature.     

Glutamine-dependent carbamyl phosphate synthetase during fetal and neonatal life in the rat

The pyrimidine-synthesizing enzyme, carbamyl phosphate synthetase II (CP synthetase II) was examined in the rat during normal fetal development and in the fed and calorically deprived neonate. CP synthetase II in the placenta, liver, gut, carcass, and brain showed the following common properties; ability to utilize ammonia as well as l-glutamine as a substrate; negligible enhancement of activity by N-acetyl l-glutamate; inhibition of activity by the glutamine analog, 6-diazo-5-oxo-l-norleucine; and by the phosphorylated pyrimidine uridine 5′-triphosphate. Apparent K_m values for l-glutamine of CP synthetase II in placenta and extrahepatic fetal structures were found to vary from 1.1 to 2.3 × 10^?5M. In the brain and placenta, tissue concentrations of l-glutamine obtained at serial time points during gestation were at least 200-fold higher. Relative activities for the enzymes catalyzing the subsequent two steps in pyrimidine biosynthesis, aspartate transcarbamylase and dihydroorotase, were substantially greater than CP synthetase II at all times measured and therefore were consistent with the possibility that CP synthetase II may be one of the rate-limiting steps in the de novo biosynthesis of pyrimidines in the placenta and extrahepatic fetal tissues. Serial observations were obtained in placenta, brain, and neonatal muscle to see whether correlations could be demonstrated between concentrations of CP synthetase II per milligram of tissue DNA and daily increments in total tissue DNA. In all these structures, higher concentrations of enzyme were observed during periods of more rapid DNA accumulation. Certain exceptions were also demonstrable. Thus, manifest CP synthetase II activity persisted in the placenta beyond day 16 of gestation (when placental DNA no longer increases); and neonatal muscle exhibited CP synthetase II activity when all net increments in DNA were abolished by caloric deprivation. The latter observations have suggested that the enzyme may be operative (and of possible regulatory significance) even in the absence of cellular proliferation.     

Microsomal electron transport. I. Reduced nicotinamide adenine dinucleotide phosphate-cytochrome c reductase and cytochrome P-450 as electron carriers in microsomal NADPH-peroxidase activity

An electron transport system that catalyzes the oxidation of NADPH by organic, hydroperoxides has been discovered in microsomal fractions. A tissue distribution study revealed that the microsomal fraction of rat liver was particularly effective in catalyzing the NADPH-peroxidase reaction whereas microsomes from adrenal cortex, lung, kidney, and testis were weakly active. The properties of the hepatic microsomal NADPH-peroxidase enzyme system were next examined in detail.The rate of NADPH oxidation by hydroperoxides was first-order with respect to microsomal protein concentration and a K_m value for NADPH of less than 3 μm was obtained. Examination of the hydroperoxide specificity revealed that cumene hydroperoxide and various steroid hydroperoxides were effective substrates for the enzyme system. Using cumene hydroperoxide as substrate, the reaction rate showed saturation kinetics with increasing concentrations of hydroperoxide and an apparent K_m of about 0.4 mm was obtained. The NADPH-peroxidase reaction was inhibited by potassium cyanide, half-maximal inhibition occurring at a cyanide concentration of 2.2 mm. NADH was able to support the NADPH-dependent peroxidase activity synergistically.Evidence compiled for the involvement of NADPH-cytochrome c reductase (NADPH-cytochrome c oxidoreductase, EC 1.6.2.3) in the NADPH-peroxidase reaction included: (1) an identical pH optimum for both activities; (2) stimulation of NADPH-peroxidase activity by increasing ionic strength; (3) inhibition by 0.05 mm, p-hydroxymercuribenzoate with partial protection by NADPH; (4) inhibition by NADP⁺; and (5) inactivation by antiserum to NADPH-cytochrome c reductase. In contrast, antibody to cytochrome b₅ did not inhibit the NADPH-peroxidase activity. Evidence for the participation of cytochrome P-450 in the NADPH-peroxidase reaction included inhibition by compounds forming type I, type II, and modified type II difference spectra with cytochrome P-450; inhibition by reagents converting cytochrome P-450 to cytochrome P-420; and marked stimulation by in vivo phenobarbital administration. The NADPH-reduced form of cytochrome P-450 was oxidized very rapidly by cumene hydroperoxide under a CO atmosphere.It was concluded that the NADPH-peroxidase enzyme system of liver microsomes is composed of the same electron transport components which function in substrate hydroxylation reactions.     

NADPH production from NADP+ using malic enzyme of Achromobacter parvulus IFO-13182

A sonicate of Achromobacter parvulus IFO-13182 produced NADPH from NADP⁺by an NADP⁺-linked malic enzyme [l-malate: NAD(P)⁺oxidoreductase, EC 1.1.1.39–40] reaction in the presence of l-malic acid and divalent metal ions. Malic enzyme of A. parvulus was stabilized by 5% l-malic acid, and activity was maintained at 60°C for 1 h. Contaminating phosphatase (orthophosphoricmonoester phosphohydrolase, EC 3.1.3.1–2) was completely inactivated by this treatment. Among the conditions tested, the optimum NADPH production was done using 36 μmol NADP⁺, 67 μmol l-malic acid, 63 μmol MgCl₂ and 1 unit of the malic enzyme in 3 ml of 55 mm phosphate buffer (pH 7.8). Conversion ratio of NADPH from NADP⁺ reached 100% after 4 h incubation at 30°C and the amount of NADPH accumulated was ～12 μmol ml^?1of the reaction mixture. No dephosphorylation of NADP⁺to NAD⁺or of NADPH to NADH was found by high performance liquid chromatography. The NADPH produced by such enzymatic reduction was purified by ethanol precipitation and dried in vacuo in powdered form with 97% purity, judged from the ratio of the absorbances at 340 and 260 nm. The purity of the NADPH produced was determined to be 95% from its coenzyme activity with NAD(P)⁺-linked glutathione reductase [NAD(P)H: oxidized-glutathione oxidoreductase, EC 1.6.4.2].     

Biosynthesis of fatty alcohols,alkane-1,2-diols and wax esters in particulate preparations from the uropygial glands of white-crowned sparrows (Zonotrichia leucophrys)

Biosynthesis of sebaceous gland waxes was studied with the uropygial gland of the white-crowned sparrow as the experimental tissue. A 27,000g particulate preparation from this gland catalyzed reduction of palmitoyl-CoA to hexadecanol at an optimum pH near 5.0 with NADPH as the preferred reductant. At low protein concentrations, palmitoyl-CoA inhibited the reductase and bovine serum albumin prevented this inhibition. An apparent K_m of 0.3 mm was calculated for palmitoyl-CoA from linear double-reciprocal plots ignoring the inhibitory concentration of the substrate. An apparent K_m of 3 mm was calculated for NADPH from linear double-reciprocal plots. Palmitoyl-CoA reduction was inhibited by thiol directed reagents such as p-chloromercuribenzoate, N-ethylmaleimide, and iodoacetamide. The particulate fraction also catalyzed esterification of hexadecanol with endogenous C₁₆ and C₁₈ acyl moieties with an optimum pH of 7.5. Stimulation of esterification of hexadecanol by ATP and CoA as well as by low concentrations of palmitoyl-CoA suggests that the CoA esters of fatty acids are involved in esterification. Tween-20 stimulated esterification of hexadecanol and hexadecyl dodecanoate was the major wax ester formed in the presence of Tween-20 suggesting that the C₁₂ acid of Tween-20 participated in esterification. Ignoring the inhibitory concentrations of hexadecanol (>0.2 mm), an apparent K_m of 0.1 mm was calculated from linear double-reciprocal plots. α-Hydroxylation of palmitic acid was demonstrated in cell-free extracts of the uropygial gland. A 27,000g particulate preparation from the gland catalyzed the reduction of α-hydroxypalmitic acid to hexadecane-1,2-diol with NADPH as the preferred reductant at an optimum pH near 6.5. This reduction required both ATP and CoA, suggesting that α-hydroxyacyl-CoA was the true substrate for the reductase. With stereospecifically labeled NADP³H, it was shown that both acyl-CoA reduction and α-hydroxy acid reduction involved transfer of the hydride specifically from the B-side of the nicotinamide ring of NADPH. Subcellular fractionation using sucrose density gradient centrifugation strongly suggested that the enzymes which catalyzed reduction of palmitoyl-CoA and α-hydroxypalmitic acid as well as the esterification of hexadecanol are localized in the microsomal membranes of the gland.     

Helicobacter pyloril-asparaginase: a promising chemotherapeutic agent

Bacterial l-asparaginases are amidohydrolases that catalyse the conversion of l-asparagine to l-aspartate and ammonia and are used as anti-cancer drugs. The current members of this class of drugs have several toxic side effects mainly due to their associated glutaminase activity. In the present study, we report the molecular cloning, biochemical characterisation and in vitro cytotoxicity of a novel l-asparaginase from the pathogenic strain Helicobacter pylori CCUG 17874. The recombinant enzyme showed a strong preference for l-asparagine over l-glutamine and, in contrast to most l-asparaginases, it exhibited a sigmoidal behaviour towards l-glutamine. The enzyme preserved full activity after 2 h incubation at 45 °C. In vitro cytotoxicity assays revealed that different cell lines displayed a variable sensitivity towards the enzyme, AGS and MKN28 gastric epithelial cells being the most affected. These findings may be relevant both for the interpretation of the mechanisms underlying H. pylori associated diseases and for biomedical applications.     

Mechanism of action of a wound-induced omega-hydroxyfatty acid:NADP oxidoreductase isolated from potato tubers (Solanum tuberosum L).

ω-Hydroxyfatty acid:NADP oxidoreductase, an enzyme involved in suberin biosynthesis, is induced by wounding potato tubers. Initial velocity and product inhibition studies with the purified enzyme suggested an ordered sequential mechanism, where NADPH is added first, followed by 16-oxohexadecanoate, and NADP is released after 16-hydroxyhexadecanoate. Substrate inhibition by NADPH was observed at concentrations higher than 0.2 mm. The inhibitory NADPH molecule competes with 16-oxohexadecanoate, indicating that it forms a dead-end complex with the E-NADPH form of the enzyme. The kinetics for the NADPH inhibition suggested that n > 1 in the rate equation $\text{v}\text{=}\text{V[NADPH]}\text{(K}{}_{\mathrm{m}}\text{+}\text{[NADPH]}\text{+}\text{[NADPH]}{}^{\mathrm{n+1}}\text{K}{}_{\mathrm{i}}\text{)}$; i.e., more than two NADPH molecules bind to enzyme. The K_m for 16-oxohexadecanoate did not change from pH 7.5 to 9.0 but increased about 10-fold from pH 9.0 to 10.0, whereas the K_m for NADPH and hexadecanal did not vary significantly in this pH range. Phenylglyoxal inactivated the enzyme; NADPH and AMP (which competes with NADPH; K_i = 1.1 mM) provided protection against such inactivation. Diethylpyrocarbonate also caused inactivation which was reversed by hydroxylamine; NADPH but not AMP protected the enzyme from this inhibition. Pyridoxal-5′-phosphate reversibly inactivated the enzyme and NaBH₄ reduction of the pyridoxal phosphate-treated enzyme resulted in irreversible inhibition; a combination of NADPH and ω-oxo C₁₆ acid provided protection against such inactivation. As the chain length of alkanals increased from C₃ to C₈, the K_m for the substrate decreased drastically from 7000 to 90μm and a further increase in chain length from C₈ to C₂₀ resulted in only a small decrease in K_m. The K_m and V for 8-oxooctanoate and 10-oxodecanoate are compared with the values obtained for 16-oxohexadecanoate. Based on these results, it is proposed that arginine acts as the binding site for NADPH, a hydrophobic crevice with lysine at the bottom forms the binding site for 16-oxohexadecanoate and histidine participates in the reaction as the proton donor.     

Effects of l-Glutamine Deprivation on Growth of HVJ (Sendai Virus) in BHK Cells

l-Glutamine requirement for viral maturation was found in BHK-HVJ cells, a cell line of baby hamster kidney cells persistently infected with HVJ (Sendai virus). Synthesis of envelope protein in BHK-HVJ cells was markedly suppressed by deprivation of l-glutamine, whereas development of nucleocapsid (S) antigen was less affected. More detailed examination of this phenomenon was carried out by using a cytolytic system. Growth of HVJ in BHK cells cultured in media deprived of various amino acids was investigated, and omission of l-glutamine from culture medium resulted in a marked inhibitory effect on the release of infectious virus and synthesis of envelope protein, although synthesis of virus-specific RNA and nucleocapsid antigen in the cells was readily detected. When l-glutamine was restored to the culture medium, infectious virus and envelope protein could be detected. l-Glutamic acid, l-aspartic acid, or l-alanine could be substituted for l-glutamine. Effects of l-glutamine deprivation on HVJ growth in several other cells were also investigated. The growth of HVJ in the cells other than BHK and FL cells was not suppressed by lack of l-glutamine. Growth of Sindbis virus in BHK cells was also markedly retarded in the absence of l-glutamine.     

Isolation and characterization of salt-tolerant glutaminases from marine Micrococcus luteus K-3

Marine Micrococcus luteus K-3 constitutively produced two salt-tolerant glutaminases, designated glutaminase I and II. Glutaminase I was homogeneously purified about approximately, 1620-fold with a 4% yield, and was a dimer with a molecular weight of about 86,000. Glutaminase II was partially purified about 190-fold with a 0.04% yield. The molecular weight of glutaminase II was also 86,000. Maximum activity of glutaminase I was observed at pH 8.0, 50°C and 8–16% NaCl. The optimal pH and temperature of glutaminase II were 8.5 and 50°C. The activity of glutaminase II was not affected by the presence of 8 to 16% NaCl. The presence of 10% NaCl enhanced thermal stability of glutaminase I. Both enzymes catalyzed the hydrolysis of l-glutamine, but not its hydroxylaminolysis. The K_m values for l-glutamine were 4.4 (glutaminase I) and 6.5 mM (glutaminase II). Neither of the glutaminases were activated by the addition of 2 mM phosphate or 2 mM sulfate. p-Chloromercuribenzoate (0.01 mM) significantly inhibited glutaminase I, but not glutaminase II. The conserved sequences LA**V and V**GGT*A were observed in the N-terminal amino acid sequences of glutaminase I, similar to that for other glutaminases.     

Inhibition of p-nitroanisole O-demethylation in perfused rat liver by potassium cyanide

The effect of potassium cyanide on p-nitroanisole O-demethylation in perfused rat livers has been examined. Cyanide (2 mm), an inhibitor of cytochrome oxidase, diminished p-nitroanisole O-demethylation by 50–75% in perfused livers from normal and phenobarbital-treated rats, but had much less effect on hepatic microsomal p-nitroanisole O-demethylation. The inhibition was also observed in livers where the activity of the pentose phosphate shunt was abolished by pretreatment with 6-aminonicotinamide. Cyanide infusion decreased hepatic $\text{ATP}\text{ADP}$ ratios and cellular concentrations of glutamate, α-ketoglutarate, and isocitrate, but caused an increase in the $\text{NADPV}{}^{\mathrm{+}}\text{NADPH}$ ratio. Rates of NADPH generation via the pentose phosphate shunt were unchanged by cyanide, and hepatic concentrations of glucose 6-phosphate were markedly increased by cyanide. Thus, inhibition of p-nitroanisole metabolism could not be explained solely by a direct interaction of cyanide with mixed-function oxidases or diminished NADPH generation via the pentose cycle. These data indicate that cyanide inhibits mixed-function oxidation in intact cells by diminishing the generation of NADPH from sources other than the pentose cycle. Further, these data are consistent with the hypothesis that some NADPH for mixed-function oxidation arises from cyanidesensitive mitochondrial sources.     

Purification and molecular and enzymic properties of mitochondrial NADH dehydrogenase.

Mitochondrial NADH dehydrogenase has been purified to homogeneity by resolution of Complex I from beef heart mitochondria with the chaotrope NaClO₄ and precipitation of the enzyme with ammonium sulfate. The enzyme is water-soluble, has a molecular weight of 69,000 ± 1000 as determined by gel filtration on Sephadex G-100 and agarose 1.5 M. It is an iron-sulfur flavoprotein, with the ratio of flavin (FMN) to nonheme iron to labile sulfide being 1:5–6:5–6. The FMN content suggests a minimum molecular weight of 74,000 ± 3000 for the enzyme. NADH dehydrogenase is composed of three subunits with apparent M_r values, as determined by acrylamide gel electrophoresis as well as by gel filtration on agarose 5 M both in the presence of sodium dodecyl sulfate, of about 51,000, 24,000, and 9–10,000. Coomassie blue stain intensities of the subunits on acrylamide gels suggest that they are present in NADH dehydrogenase in equimolar amounts. However, summation of the apparent M_r values of the dodecyl sulfate-treated subunits appears to overestimate the molecular weight of the native enzyme. The amino acid compositions of NADH dehydrogenase and of each of the isolated and purified subunits have been determined. NADH dehydrogenase catalyzes the oxidation of NADH and NADPH by quinones, ferric compounds, and NAD (3-acetylpyridine adenine dinucleotide was used). All the activities of NADH dehydrogenase are greatly stimulated by addition of guanidine (up to 150 mm), alkylguanidines, arginine, and arginine methyl ester to the assay medium. Phosphoarginine had no effect. These results pointed to the importance of the positively charged guanido group, which appears to interact with and neutralize the negative charges on NAD(P)H and thereby allow for better enzyme-substrate interaction. In the absence of guanidine, NADPH is essentially unoxidized by the enzyme at pH values above 6.0. However, both NADPH dehydrogenase and NADPH → NAD transhydrogenase activities increase dramatically as the assay pH is lowered below pH = 6. Since the pK of the 2′-phosphate of NADPH is 6.1, it appears that the above pH effect is related to protonation of the 2′-phosphate, thus rendering NADPH a closer electronic analog of NADH, which is the primary substrate of the enzyme.     

Enzymatic synthesis of β-N-(γ-l(+)-glutamyl)-4-carboxyphenylhydrazine with Escherichia coli γ-glutamyltransferase

A new method for the synthesis of β-N-(γ-l(+)-glutamyl)-4-carboxyphenylhydrazine, a precursor of agaritine, is presented. This compound was prepared from l-glutamine and 4-hydrazinobenzoic acid through the transpeptidation reaction catalyzed by the Escherichia coli γ-glutamyltransferase. The optimum reaction conditions for the production of β-N-(γ-l(+)-glutamyl)-4-carboxyphenylhydrazine were 50 mM l-glutamine, 500 mM 4-hydrazinobenzoic acid and 40 U γ-glutamyltransferase/mL at pH 8 and 37 °C for 24 h. The product was obtained with a conversion rate of 90% (mol/mol). γ-Glutamyltransferase activity was not inhibited by 4-hydrazinobenzoic acid at concentrations up to 1000 mM. This simple and efficient method would facilitate the synthesis of glutamyl phenylhydrazine analogs, including agaritine.     

NADPH fluorescence in the cyanobacterium Synechocystis sp. PCC 6803: A versatile probe for in vivo measurements of rates,yields and pools

We measured the kinetics of light-induced NADPH formation and subsequent dark consumption by monitoring in vivo its fluorescence in the cyanobacterium Synechocystis PCC 6803. Spectral data allowed the signal changes to be attributed to NAD(P)H and signal linearity vs the chlorophyll concentration was shown to be recoverable after appropriate correction. Parameters associated to reduction of NADP⁺ to NADPH by ferredoxin–NADP⁺-oxidoreductase were determined: After single excitation of photosystem I, half of the signal rise is observed in 8 ms; Evidence for a kinetic limitation which is attributed to an enzyme bottleneck is provided; After two closely separated saturating flashes eliciting two photosystem I turnovers in less than 2 ms, more than 50% of the cytoplasmic photoreductants (reduced ferredoxin and photosystem I acceptors) are diverted from NADPH formation by competing processes. Signal quantitation in absolute NADPH concentrations was performed by adding exogenous NADPH to the cell suspensions and by estimating the enhancement factor of in vivo fluorescence (between 2 and 4). The size of the visible (light-dependent) NADP (NADP⁺ + NADPH) pool was measured to be between 1.4 and 4 times the photosystem I concentration. A quantitative discrepancy is found between net oxygen evolution and NADPH consumption by the light-activated Calvin–Benson cycle. The present study shows that NADPH fluorescence is an efficient probe for studying in vivo the energetic metabolism of cyanobacteria which can be used for assessing multiple phenomena occurring over different time scales.     

Production of l-Glutamine by a Penicillin-Resistant Mutant of Flavobacterium rigense

To establish a practical method for the fermentative production of l-glutamine, cultural conditions for the accumulation of a large amounts of l-glutamine were investigated by using Flavobacterium rigense 703, which was previously reported by us as a l-glutamine-producing mutant. As a result, a yield of 25 mg of l-glutamine per ml was obtained after a 48-h cultivation in a medium containing glucose, yeast extract, (NH(4))(2)-fumarate, KH(2)PO(4), K(2)HPO(4), MgSO(4).7H(2)O, and CaCO(3) (pH 6.4). Accumulation of l-glutamine was dependent upon the concentration of (NH(4))(2)-fumarate, and a suboptimum growth at a relatively high concentration of (NH(4))(2)-fumarate was essential for the maximum production of l-glutamine. At the optimum conditions, glutamic acid was formed as a by-product at a concentration of less than 1 mg/ml, but accumulation of the other amino acids was negligible. The product was isolated from the culture broth and readily purified by anion-exchange chromatography. The pure crystals of l-glutamine obtained in an 80% yield were optically and chromatographically pure.