Dimethylsulfide:acceptor oxidoreductase from Rhodobacter sulfidophilus. The purified enzyme contains b-type haem and a pterin molybdenum cofactor

Dimethylsulfide:receptor oxidoreductase was purified from the purple non-sulfur phototrophic bacterium Rhodobacter sulfidophilus. The native form of the enzyme had a molecular mass of 152 kDa and was composed of three distinct subunits of 94, 38 and 32 kDa. Dimethylsulfide:acceptor oxidoreductase did not oxidise other thioethers which were tested. The enzyme was able to reduce a variety of N-oxides using reduced methylviologen as electron donor but it reduced dimethylsulfoxide at a very low rate. The resting form of dimethylsulfide:acceptor oxidoreductase exhibited a spectrum which was characteristic of a reduced cytochrome with absorbance maxima at 562 nm, 533 nm and 428 nm. Pyridine haemochrome analysis established that the cytochrome contained a b-type haem and a content of 0.65 mol protohaem/mol enzyme was determined. After oxidation of the haem with ferricyanide, the absorbance spectrum of the reduced cytochrome was restored by reduction with dimethylsulfide. Metal analysis revealed that dimethylsulfide:acceptor oxidoreductase contained 0.5 mol Mo and 3.5 mol Fe/mol enzyme. Heat treatment of the enzyme released material with fluorescence excitation and emission spectra which were characteristic of form B of the pterin component of the pterin molybdenum cofactor. From this analysis it is concluded that dimethylsulfide:acceptor oxidoreductase is a molybdenum oxotransferase which may also contain a iron-sulfur cluster. It is suggested that the haem and pterin molybdenum cofactor are associated with the 94-kDa subunit.

Two amine oxidases from Aspergillus niger AKU 3302 contain topa quinone as the cofactor: unusual cofactor link to the glutamyl residue occurs only at one of the enzymes

Amine oxidases (EC 1.4.3.6) from Aspergillus niger, AO-I (2 x 75 kDa) and AO-II (80 kDa), were examined to determine the cofactor structure. Inactivated with p-nitrophenylhydrazine, they showed absorption and fluorescence spectra similar to those published for other copper amine oxidases and to topa hydantoin p-nitrophenylhydrazone. After digestion by thermolysin and pronase, cofactor peptides were purified by HPLC and sequenced. For thermolytic peptides, a typical topa consensus sequence, Asn-X-Glu-Tyr, was obtained for AO-II, although in case of AO-I it overlapped with Val-Val-Ile-Glu-Pro-Tyr-Gly. For pronase peptides of AO-I, only the latter sequence was obtained. NMR and mass spectroscopy confirmed the residue X as topa p-nitrophenylhydrazone in AO-II and revealed the presence of a residue Z attached to the Glu in the peptide Val-Val-Ile-Glu(Z)-Pro of AO-I. This residue was separated from the peptide by hydrolysis and identified as a product derived from topa quinone. The data, together with amino-acid sequence of AO-I, confer strong evidence for topa quinone as the cofactor, bound in the typical consensus sequence. Raman spectra of the p-nitrophenylhydrazone derivative of AO-I and its pronase peptide showed essentially the same peaks matching to a model compound for topa p-nitrophenylhydrazone. However, there may exist an unusual ester link between the topa-404 and Glu-145 in the native enzyme.

A novel automated assay for malate dehydrogenase isoenzymes

We have developed a new automated method for the determination of malate dehydrogenase (MDH) isoenzymes in serum employing guanidine hydrochloride. Our proposed method showed good reproducibility; within-run precision coefficient of variations (CVs) were less than 2.5 (mean 13.6-42.9 U/L) for total MDH (T-MDH) and less than 6.7% (mean 6.3-23.5 U/L) for mitochondrial MDH (m-MDH) (n = 10). The upper detection limit of the proposed method exhibited good linearity up to 1,000 U/L for both T-MDH and m-MDH. In the proposed m-MDH reagent, the presence of up to 2,000 U/L of cytosolic MDH(c-MDH) activity had no effect on the outcome of m-MDH assay. Results of our proposed method (y) correlated well with those of the electrophoretic method (x) giving the regression equation: y = 1.46 x + 6.87 (N = 30); r = 0.99. Normal concentrations of various anticoagulants and bilirubin did not affect the assay results. Both ascorbic acid and glucose exhibited a slight positive interference with the proposed assay. Clinically, we found that m-MDH activity in serum had greater diagnostic predictive value than T-MDH activity for judging successful outcome of reperfusion therapy; the prognosis was poor when the m-MDH/T-MDH ratio was greater than 20%.

Generation mechanism and purification of an inactive form convertible in vivo to the active form of quinoprotein alcohol dehydrogenase in Gluconobacter suboxydans

Alcohol dehydrogenase (ADH) of acetic acid bacteria is a membrane-bound quinohemoprotein-cytochrome c complex involved in vinegar production. In Gluconobacter suboxydans grown under acidic growth conditions, it was found that ADH content in the membranes was largely increased but the activity was not much changed, suggesting that such a condition produces an inactive form of ADH (inactive ADH). A similar phenomenon could be also observed in Acetobacter aceti, another genus of acetic acid bacteria. Furthermore, aeration conditions were also shown to affect ADH production; the ADH level was increased and was present as an active form under low-aeration conditions, while the ADH level was decreased and was present mainly as an inactive form under high-aeration conditions. Inactive ADH was solubilized from the membranes of G. suboxydans grown in acidic and high-aeration conditions and was purified separately from the normal, active form of ADH (active ADH). In spite of having 10 times less enzyme activity than active ADH, inactive ADH could not be distinguished from active ADH with respect to their subunit compositions, molecular sizes, and prosthetic groups. Inactive ADH, however, had a relatively loose conformation with a partially oxidized state, while active ADH had a tight conformation with a completely reduced state, suggesting that inactive ADH may lack a right subunit's interaction and that one of the heme c components may be inactivated. Reactivation from such an inactive ADH occurred either by shifting of the pH of the culture medium up during the cultivation or by incubation of the resting cells at the neutral pH region in the presence of an energy source such as D-sorbitol. Such an activation of ADH was repressed by the addition of a proton uncoupler and could not occur in the spheroplasts. Thus, the results suggest that inactive ADH could be generated abundantly under acidic growth conditions and converted to the active form at a neutral culture pH. The data also suggest that some periplasmic component may be involved in the conversion of inactive ADH into the active form by consuming some forms of energy.

Limited proteolysis of Hansenula polymorpha yeast amine oxidase: isolation of a C-terminal fragment containing both a copper and quino-cofactor

Limited proteolysis of recombinant Hansenula polymorpha yeast amino oxidase produces a 48 kDa fragment which corresponds to the C-terminal two-thirds of the protein. The fragment contains both TOPA (2,4,5-trihydroxyphenylalanine) and copper, as well as the histidine ligands implicated in copper binding. The fragment is proposed to be the domain responsible for cofactor production in yeast amine oxidase.

Levels of pyrroloquinoline quinone in various foods

The levels of free pyrroloquinoline quinone (PQQ) in various foods were examined by the use of gas chromatography-mass spectrometry. PQQ was extracted from the samples, after addition of [U-13C]PQQ as internal standard, with n-butanol and Sep-Pak C18 cartridges. After derivatization of PQQ with phenyltrimethylammonium hydroxide, molecular peaks at m/z 448 and 462 were used for detection of PQQ and [U-13C]PQQ respectively, by selected ion monitoring. Free PQQ could be detected in every sample in the range 3.7-61 ng/g or ng/ml. Since its levels in human tissues and body fluids are 5-10 times lower than those found in foods, it is probable that PQQ existing in human tissues is derived, at least partly, from the diet.

Production and application of monoclonal antibodies specific to pyrroloquinoline quinone

We produced five monoclonal antibodies (mAbs 1, 2, 6, 7, and 9) that are specific to pyrroloquinoline quinone (PQQ). PQQ-conjugated hemocyanin was used for the immunization of mice and the hybridomas were selected using PQQ-conjugated BSA in an enzyme-linked immunosorbent assay. MAbs 2 and 9 were of the IgG1 isotype. Both could recognize free PQQ, the former probably at the o-quinone and the latter at the opposite side of the molecule. They did not bind with trihydroxyphenylalanine, dihydroxyphenylalanine, 1,2,4-trihydroxybenzene, ascorbic acid, riboflavin, or menadione. In contrast to the IgGs, mAbs 1, 6, and 7 (IgMs) did not bind with free PQQ. Using mAb 2, a competitive enzyme-linked immunosorbent assay was developed, which enabled us to determine 50 nM-1 microM free PQQ. Furthermore, we analyzed the covalently bound prosthetic groups of two quinoproteins (amine oxidase from Aspergillus niger and amine dehydrogenase from Pseudomonas putida) by Western analysis using these mAbs. However, the results was negative, indicating that the prosthetic groups are not PQQ.

Identification of molybdopterins in molybdenum- and selenium-containing enzymes

Selenium is coordinated to a molybdenum atom in nicotinic acid hydroxylase (NAH) from Clostridium barkeri and formate dehydrogenase H (FDH) from Escherichia coli. Selenium is present in FDH in a selenocysteine residue whereas in NAH in occurs in an unidentified labile cofactor. In this paper we describe a simple procedure for isolation and identification of molybdopterins from Mo-containing enzymes. The molybdopterin, after release from the protein with guanidine-hydrochloride, is reduced with KBH4, alkylated with iodoacetamide and separated on a reverse-phase HPLC column. The carboxam-idomethylated pterin compound is further characterized by UV spectroscopy and mass-spectrometry. We found that FDH contains molybdopterin guanine dinucleotide whereas NAH contains molybdopterin cytosine dinucleotide.

Vibrio harveyi NADPH-flavin oxidoreductase: cloning, sequencing and overexpression of the gene and purification and characterization of the cloned enzyme

NAD(P)H-flavin oxidoreductases (flavin reductases) from luminous bacteria catalyze the reduction of flavin by NAD(P)H and are believed to provide the reduced form of flavin mononucleotide (FMN) for luciferase in the bioluminescence reaction. By using an oligonucleotide probe based on the partial N-terminal amino acid sequence of the Vibrio harveyi NADPH-FMN oxidoreductase (flavin reductase P), a recombinant plasmid, pFRP1, was obtained which contained the frp gene encoding this enzyme. The DNA sequence of the frp gene was determined; the deduced amino acid sequence for flavin reductase P consists of 240 amino acid residues with a molecular weight of 26,312. The frp gene was overexpressed, apparently through induction, in Escherichia coli JM109 cells harboring pFRP1. The cloned flavin reductase P was purified to homogeneity by following a new and simple procedure involving FMN-agarose chromatography as a key step. The same chromatography material was also highly effective in concentrating diluted flavin reductase P. The purified enzyme is a monomer and is unusual in having a tightly bound FMN cofactor. Distinct from the free FMN, the bound FMN cofactor showed a diminished A375 peak and a slightly increased 8-nm red-shifted A453 peak and was completely or nearly nonfluorescent. The Kms for FMN and NADPH and the turnover number of this flavin reductase were determined. In comparison with other flavin reductases and homologous proteins, this flavin reductase P shows a number of distinct features with respect to primary sequence, redox center, and/or kinetic mechanism.

Cofactor contents of methanogenic bacteria reviewed

The content of specific methanogenic cofactors was assessed for a range of hydrogenotrophic and methylotrophic methanogenic bacteria grown on different substrates using high performance liquid chromatography. In general, all methanogens were found to contain coenzyme F420 analogues, methanopterin (MPT) analogues and 5-hydroxybenzimidazolylcobamide (vitamin B12-HBI). In hydrogenotrophic methanogens of the genera Methano-bacterium and Methanobrevibacter, as a rule, coenzymes F420-2 and F420-3 as well as MPT were present. Members of the closely related genera Methanospirillum, Methanogenium, Methanoculleus and Methanoplanus contained the same coenzyme F420 analogues but tatiopterin and/or thermopterin were present instead of MPT. In contrast, methylotrophic methanogens predominantly contained coenzymes F420-5 and F420-4, and sarcinapterin (SPT). In Methanolobus tindarius, both MPT and SPT were found, whereas no MPT analogue could be detected in Methanosphaera stadtmanae. In the hydrogenotroph Methanococcus voltae, SPT occurred as the sole MPT analogue. The levels of the various cofactors varied markedly among different methanogens and also for individual methanogens as a function of growth substrate or batch number. A correlation of cofactor levels and substrate utilized was not established. However, with methylotrophic methanogens it was noticed that the ratio of the contents of vitamin B12-HBI and SPT was independent of growth substrate.

Failure to verify high levels of pyrroloquinoline quinone in eggs and skim milk

The levels of pyrroloquinoline quinone (PQQ) in eggs, skim milk and milk was re-examined by the use of gas chromatography/mass spectrometry. PQQ was extracted from the samples, after addition of [U-13C]PQQ as internal standard, with n-butanol and Sep-Pak C18 cartridges. After derivatization of PQQ with phenyltrimethylammonium hydroxide, molecular peaks at m/z 448 and 462 were used for detection of PQQ and [U-13C]PQQ, respectively, by selected ion monitoring. PQQ could be detected in eggs, skim milk and milk, but their levels were very low (e.g., egg yolk: 7.0 ng/ml; skim milk: 2.5 ng/g dry weight). Our data for eggs and skim milk are far below those measured by the redox cycling method of Gallop's group.

Purification and characterization of NADH oxidase from Serpulina (Treponema) hyodysenteriae

NADH oxidase (EC 1.6.99.3) was purified from cell lysates of Serpulina (Treponema) hyodysenteriae B204 by differential ultracentrifugation, ammonium sulfate precipitation, and chromatography on anion-exchange, dye-ligand-affinity, and size-exclusion columns. Purified NADH oxidase had a specific activity 119-fold higher than that of cell lysates and migrated as a single band during denaturing gel electrophoresis (sodium dodecyl sulfate-polyacrylamide gel electrophoresis [SDS-PAGE]). The enzyme was a monomeric protein with an estimated molecular mass of 47 to 48 kDa, as determined by SDS-PAGE and size-exclusion chromatography. Optimum enzyme activity occurred in buffers with a pH between 5.5 and 7.0. In the presence of oxygen, beta-NADH but not alpha-NADH, alpha-NADPH, or beta-NADPH was rapidly oxidized by the enzyme (Km = 10 microM beta-NADH; Vmax = 110 mumol beta-NADH min-1 mg of protein-1). Oxygen was the only identified electron acceptor for the enzyme. On isoelectric focusing gels, the enzyme separated into three subforms, with isoelectric pH values of 5.25, 5.35, and 5.45. Purified NADH oxidase had a typical flavoprotein absorption spectrum, with peak absorbances at wavelengths of 274, 376, and 448 nm. Flavin adenine dinucleotide was identified as a cofactor and was noncovalently associated with the enzyme at a molar ratio of 1:1. Assays of the enzyme after various chemical treatments indicated that a flavin cofactor and a sulfhydryl group(s), but not a metal cofactor, were essential for activity. Hydrogen peroxide and superoxide were not yielded in significant amounts by the S. hyodysenteriae NADH oxidase, indirect evidence that the enzyme produces water from reduction of oxygen with NADH. The N-terminal amino acid sequence of the NADH oxidase was determined to be MKVIVIGCHGAGTWAAK. In its biochemical properties, the NADH oxidase of S. hyodysenteriae resembles the NADH oxidase of another intestinal bacterium, Enterococcus faecalis.

Quantitation of molybdopterin oxidation product in wild-type and molybdenum cofactor deficient mutants of Chlamydomonas reinhardtii

A simple and reliable procedure of oxidation of molybdenum cofactor (MoCo) from molybdoenzymes by autoclaving samples at 120 degrees C for 20 min yielded a single predominant fluorescent species that could be quantitatively determined by reverse phase high performance liquid chromatography. This method allowed detection and quantitation of molybdopterin in cell-free extracts of the green alga Chlamydomonas reinhardtii. The MoCo oxidation product from C. reinhardtii has the same chromatographic and spectral properties as that of milk xanthine oxidase and chicken liver sulfite oxidase. The oxidized species was also detected in molybdenum cofactor mutants of Chlamydomonas reinhardtii defective at the nit-3, nit-4, nit-5/nit-6 and nit-7 loci, which strongly suggests that active molybdenum cofactor itself is not directly involved in the control of its own biosynthetic pathway.

Trace levels of pyrroloquinoline quinone in human and rat samples detected by gas chromatography/mass spectrometry

A detailed procedure for the assay of free pyrroloquinoline quinone (PQQ) in human and rat samples by gas chromatography/mass spectrometry (GC/MS) has been established with stable-isotopic PQQ as internal standard. PQQ was extracted from the samples, after addition of the internal standard, with butanol under acid conditions and with Sep-Pak C18 cartridges. After derivatization of PQQ with phenyltrimethylammonium hydroxide, molecular peaks at m/z 448 and 462 were used for detection of PQQ and [U-13C]PQQ by selected ion monitoring, respectively. Trace amounts of free PQQ were detected in eight organs, plasma and urine of the human, and in three organs of the rat. The PQQ level was highest in the human spleen (5.9 +/- 3.4 ng/g tissue, followed by the pancreas and lung, and it was below detection limits for human brain and heart. Trace levels of PQQ were also found in rat small intestine, liver and testis. Our data are far below those measured by the redox cycling method of Gallop's group for human plasma, adrenal and urine.

Identification of topaquinone and its consensus sequence in copper amine oxidases

The nature of the active site cofactor and the amino acid sequence flanking this structure have been determined in a range of copper amine oxidases. For enzymes from porcine plasma, porcine kidney, and pea seedlings, proteolytic digestion was performed on phenylhydrazone or p-nitrophenylhydrazone derivatives. Thermolysin treatment leads to relatively small active site peptides, which have been characterized by Edman degradation and by resonance Raman spectroscopy. Resonance Raman spectra of peptides show identical peak positions and intensities relative to each other and to a model p-nitrophenylhydrazone derivative of topaquinone hydantoin, establishing topaquinone as the cofactor in each instance. Edman degradation of peptides provides active site sequences for comparison to previous determinations with bovine serum and yeast amine oxidases. The available data establish a consensus sequence of Asn, Topa, Asp/Glu. Trypsin leads to significantly longer peptides, which reveal a high degree of sequence identity between plasma proteins from bovine and porcine sources (89%), with significantly decreased identity between the porcine serum and intracellular amine oxidases (56%). A lower degree of identity (45%) is observed between the pea seedling and mammalian enzymes. As an alternative to the isolation of active site peptides for topaquinone identification, visible spectra of intact proteins have been investigated. It is shown that p-nitrophenylhydrazone derivatives of native enzymes, active site-derived peptides, and a topaquinone model exhibit identical behavior, absorbing at 457-463 nm at neutral pH (pH 7.2) and at 575-587 nm in basic solution (1-2 M KOH). These spectral properties, which appear unique to topaquinone, provide a rapid and simple test for the presence of this cofactor in intact enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain glutamate decarboxylase and pyrroloquinoline quinone

Porcine brain glutamate decarboxylase was examined for the presence of covalently bound pyrroloquinoline quinone (PQQ). HPLC analysis of pure glutamate decarboxylase subjected to the hexanol extraction procedure gave negative results when monitored at 320 nm, the maximum of absorbance of 4-hydroxy-5-hexoxy-PQQ. Resolved glutamate decarboxylase exhibits a structureless absorption band at wavelengths longer than 300 nm which cannot be attributed to PQQ. The holoenzyme is not a pyridoxal-quinoprotein; its catalytic mechanism involves the participation of only one cofactor, i.e. pyridoxal-5-P. Free PQQ is a strong inhibitor of the decarboxylase (Ki = 13 microM) and the reaction with the protein results in spectral changes resembling those of polylysine treated with PQQ. If the concentration of free PQQ in some regions of the brain reaches the micromolar level, then PQQ might play a role in the regulation of glutamate decarboxylase activity.