Presence Of Pyrroloquinoline Quinone Research Articles

Isolation and characterization of the moxJ, moxG, moxI, and moxR genes of Paracoccus denitrificans: inactivation of moxJ, moxG, and moxR and the resultant effect on methylotrophic growth.

By using the moxF gene encoding the large fragment of methanol dehydrogenase as a probe, a downstream linked chromosomal fragment was isolated from a genomic bank of Paracoccus denitrificans. The nucleotide sequence of the fragment was determined and revealed the 3' part of moxF, four additional open reading frames, and the 5' part of a sixth one. The organization and deduced amino acid sequences of the first three frames downstream from moxF were found to be largely homologous to the moxJ, moxG, and moxI gene products of Methylobacterium extorquens AM1. Directly downstream from these three genes, a new mox gene was identified. The gene is designated moxR. By using the suicide vector pGRPd1, the moxJ, moxG, and moxR genes were inactivated by the insertion of a kanamycin resistance gene. Subsequently, suicide vector pRVS1 was used to replace the marker genes in moxJ and moxG for unmarked deletions made in vitro. As a result, the three insertion strains as well as the two unmarked mutant strains were unable to grow on methanol, even in the presence of pyrroloquinoline quinone. Growth on succinate and on methylamine was not affected. In all five mutant strains, synthesis of the large subunit of methanol dehydrogenase and of inducible cytochrome c553i was observed. The moxJ and moxG insertion mutant strains were unable to synthesize both the cytochrome c551i and the small subunit of methanol dehydrogenase, and this lack of synthesis was attended by the loss of methanol dehydrogenase activity. The moxJ deletion mutant strain partly synthesized the latter two proteins, cytochrome c551i. Partial synthesis of the small subunit of methanol dehydrogenase observed with the latter strain was attended by a corresponding extent of methanol dehydrogenase activity. The moxR insertion mutant strain was shown to synthesize cytochrome c551i as well as the large and small subunits of methanol dehydrogenase, but no methanol dehydrogenase activity was observed. The results show that periplasmic cytochrome c551i is the moxG gene product and the natural electron acceptor of methanol dehydrogenase in P. denitrificans. In contrast to earlier suggestions, this cytochrome was found to be different from membrane-bound cytochrome c552. In addition, it is demonstrated that moxI encodes the small subunit of methanol dehydrogenase. It is suggested that MoxJ is involved in the assemblage of active methanol dehydrogenase in the periplasm and, in addition, that MoxR is involved in the regulation of formation of active methanol dehydrogenase.

An investigation on the quinoprotein nature of some fungal and plant oxidoreductases.

The presence of pyrroloquinoline quinone (PQQ) as the organic cofactor of Dactylium dendroides galactose oxidase and lentil (Lens culinaris) seedling amine oxidase, purported PQQ-containing oxidoreductases (Van der Meer, R. A., Jongejan, J. A., and Duine, J. A. (1989) J. Biol. Chem. 264, 7792-7794; Citro, G., Verdina, A., Galati, R., Floris, G., Sabatini, S., and Finazzi-Argo', A. (1989) FEBS Lett. 247, 201-204), was reinvestigated using the nitro blue tetrazolium redoxcycling method (Paz, M. A., Gallop, P. M., Torrelio, B. M., and Flückiger, R. (1988) Biochem. Biophys. Res. Commun. 154, 1330-1337; Paz, M. A., Flückiger, R., Boak, A., Kagan, H. M., and Gallop, P. M. (1991) J. Biol. Chem. 266, 689-692) and the enzyme-linked immunosorbent assay with polyclonal antibodies against PQQ. The possible quinoprotein nature of the laccases from Polyporus versicolor and Rhus vernicifera was also investigated because of the similarities in spectroscopic and kinetic features of these enzymes and the laccase from Phlebia radiata, reported to be a PQQ protein (Karhunen, E., Niku-Paavola, M.-L., Viikari, L., Haltia, T., Van der Meer, R. A., and Duine, J. A. (1990) FEBS Lett. 267, 6-8). The presence of a quinonoid cofactor in lentil seedling amine oxidase is confirmed, whereas galactose oxidase and both laccases do not display any quinoprotein nature.

Cataract Induction by 1,2-Naphthoquinone I. Studies on the Redox Properties of Bovine Lens Proteins

Conditions of oxidative stress may lead to cataract formation. Reaction of certain flavoproteins, the NADH: oxidoreductases, with different quinones is well known to form hydrogen-peroxide. This reaction was investigated to get more information on cataract induction by naphthalene and its quinone metabolites. Protein extracts from bovine lens cortex exhibit "diaphorase" activity, indicated as dye reduction in the presence of NADH and dichlorophenol-indophenol (DCPIP) or ferricyanide. Different redox cycling compounds are shown to be active in this "diaphorase" reaction by lens protein extract (LCE): Oxygen consumption can be detected in the presence of pyrroloquinoline quinone and juglone whereas 1,4-naphthoquinone, menadione and paraquat are no redox cyclists in this flavoprotein catalyzed reaction.

Quantitative aspects of glucose metabolism by Escherichia coli B/r, grown in the presence of pyrroloquinoline quinone.

Escherichia coli B/r was grown in chemostat cultures under various limitations with glucose as carbon source. Since E. coli only synthesized the glucose dehydrogenase (GDH) apo-enzyme and not the appropriate cofactor, pyrroloquinoline quinone (PQQ), no gluconate production could be observed. However, when cell-saturating amounts of PQQ (nmol to mumol range) were pulsed into steady state glucose-excess cultures of E. coli, the organisms responded with an instantaneous formation of gluconate and an increased oxygen consumption rate. This showed that reconstitution of GDH in situ was possible. Hence, in order to examine the influence on glucose metabolism of an active GDH, E. coli was grown aerobically in chemostat cultures under various limitations in the presence of PQQ. It was found that the presence of PQQ indeed had a sizable effect: at pH 5.5 under phosphate- or sulphate-limited conditions more than 60% of the glucose consumed was converted to gluconate, which resulted in steady state gluconate concentrations up to 80 mmol/l. The specific rate of gluconate production (0.3-7.6 mmol.h-1.(g dry wt cells)-1) was dependent on the growth rate and the nature of the limitation. The production rate of other overflow metabolites such as acetate, pyruvate, and 2-oxoglutarate, was only slightly altered in the presence of PQQ. The fact that the cells were now able to use an active GDH apparently did not affect apo-enzyme synthesis.

Reversible thermal inactivation of the quinoprotein glucose dehydrogenase from Acinetobacter calcoaceticus. Ca2+ ions are necessary for re-activation

The soluble form of the homogeneous quinoprotein glucose dehydrogenase from Acinetobacter calcoaceticus is reversibly inactivated at temperatures above 35 degrees C. An equilibrium is established between active and denatured enzyme, this depending on the protein concentration and the inactivation temperature used. Upon thermal inactivation the enzyme dissociates into the prosthetic group pyrroloquinoline quinone and the apo form of glucose dehydrogenase. After inactivation at 50 degrees C active enzyme is re-formed again at 25 degrees C. Ca2+ ions are necessary for the re-activation process. The velocity of re-activation depends on the protein concentration, the concentration of the prosthetic group pyrroloquinoline quinone and the Ca2+ concentration. The apo form of glucose dehydrogenase can be isolated, and in the presence of pyrroloquinoline quinone and Ca2+ active holoenzyme is formed. Even though native glucose dehydrogenase is not inactivated in the presence of EDTA or trans-1,2-diaminocyclohexane-NNN'NH-tetra-acetic acid, Ca2+ stabilizes the enzyme against thermal inactivation. Two Ca2+ ions are found per subunit of glucose dehydrogenase. The data suggest that pyrroloquinoline quinone is bound at the active site via a Ca2+ bridge. Mn2+ and Cd2+ can replace Ca2+ in the re-activation mixture.

Characterization of nitrile hydratase and amidase, which are responsible for the conversion of dinitriles to mononitriles, from Corynebacterium sp.

Two enzymes, nitrile hydratase and amidase, which participate in the conversion of trans-1,4- dicyanocyclohexane (t-DCC) to frans-4-cyanocyclohexane-l-carboxylic acid (t-MCC), a tranexamic acid intermediate, were purified and characterized. Nitrile hydratase was obtained in a homogeneous state. The molecular weight of the native enzyme was 61,400 and that of the subunit 26.900, indicating a dimer structure. Valeronitrile and butyronitrile were good substrates for the enzyme. The enzyme could also hydrate benzonitrile, p-hydroxybenzonitrile and 4-cyanobenzoic acid. t-DCC was ex-clusively hydrated to fnzws-4-cyanocycIohexane-l-car boxy amide (t-MCMA), further hydration of the nitrile group of t-MCMA and t-MCC not being observed. The presence of pyrroloquinoline quinone in the enzyme was confirmed. The presence of iron was also confirmed. The amidase of the strain was also purified. The latter enzyme could hydrate t-MCMA, yielding t-MCC. The enzyme was highly resistant to SH reagents.

Physiological properties of a pyrroloquinoline quinone mutant ofMethylobacterium organophilum

The grwoth of MTMl, a mutant of methylobacterium organophilum) blocked in the use of methanol as a carbon and energy source, was restored by addition of pyrroloquinoline quinone (PQQ) in the culture medium. No PQQ could be detected in crude medium. No PQQ could be of MTMl. Therefore, MTMl can be regarded as a mutant blocked in the biosynthesis of PQQ. Under the conditions of growth employed, growth rates of MTMl on methanol, comparable to those of the wild type, occured at a PQQ concentration of 1 μM. Since lower amounts of methanol dehydrogenase (MDH) wer found in cell-free extracts of PQQ-supplemented MTMl, the wild type strain synthesizes a surplus of MDH under these conditions. Growth of M. organophilum on ethanol proceeds via MDH as a catalyst for the first step, since (NAD(P) -dependent etanol. dehydrogenase was absent in cell-free extracts and growth of MTMl on ethanol only took place in the presence of PQQ. On the hand, growth of MTMl on mthylamine was unimpaired. This is in accordance with the fact that methylamine dehydrogenase was absent and N-methylamine mate dehydrogenase was present in cell-free extracts

Physiological properties of a pyrroloquinoline quinone mutant of Methylobacterium organophilum

The grwoth of MTMl, a mutant of Methylobacterium organophilum) blocked in the use of methanol as a carbon and energy source, was restored by addition of pyrroloquinoline quinone (PQQ) in the culture medium. No PQQ could be detected in crude medium. No PQQ could be of MTMl. Therefore, MTMl can be regarded as a mutant blocked in the biosynthesis of PQQ. Under the conditions of growth employed, growth rates of MTMl on methanol, comparable to those of the wild type, occured at a PQQ concentration of 1 µM. Since lower amounts of methanol dehydrogenase (MDH) wer found in cell-free extracts of PQQ-supplemented MTMl, the wild type strain synthesizes a surplus of MDH under these conditions. Growth of M. organophilum on ethanol proceeds via MDH as a catalyst for the first step, since (NAD(P) -dependent etanol. dehydrogenase was absent in cell-free extracts and growth of MTMl on ethanol only took place in the presence of PQQ. On the hand, growth of MTMl on mthylamine was unimpaired. This is in accordance with the fact that methylamine dehydrogenase was absent and N-methylglutamate dehydrogenase was present in cell-free extracts.

Bacterial NAD(P)-independent quinate dehydrogenase is a quinoprotein

Acinetobacter calcoaceticus LMD 79.41 produced significant amounts of pyrrolo-quinoline quinone (PQQ) in its culture medium when grown on quinic acid or shikimic acid. Studies with LMD 79.41 and PQQ- -mutants of this strain demonstrated that this organism contains an NAD(P)-independent quinate dehydrogenase (QDH) (EC 1.1.99.-), catalyzing the first degradation step of these compounds, and that the enzyme contains PQQ as a cofactor, i.e. is a quinoprotein. Synthesis of QDH was induced by protocatechuate and the enzyme appeared to be particle-bound. Acinetobacter Iwoffi RAG-1 produced a quinoprotein QDH apoenzyme since growth on quinic acid only occurred in the presence of PQQ. The results obtained with the PQQ- -mutants of strain LMD 79.41 also provided some insight into the regulation of PQQ biosynthesis and assemblage of quinoprotein enzymes in the periplasmic space. Since two species of Pseudomonas also contained a quinoprotein QDH, it is assumed that bacterial NAD(P)-independent quinate dehydrogenase is a quinoprotein.

Dopamine β-hydroxylase from bovine adrenal medulla contains covalently-bound pyrroloquinoline quinone

Treatment of homogeneous dopamine β-hydroxylase (DBH) preparations from bovine adrenals with the inhibitor phenylhydrazine (PH) changed the structureless absorption spectrum of DBH into spectra with a maximum at 350 nm. A product with this absorption spectrum could be detached with pronase, enabling its isolation. It appeared to be the C(5) hydrazone of pyrroloquinoline quinone (PQQ) and PH, as judged from its properties and the fact that it could be transformed into PQQ itself. From the yield obtained a ratio of 0.85 PQQ per enzyme subunit was calculated. In contrast to copper-quinoprotein amine oxidases (EC 1.4.3.6), hydrazone formation in DBH did not require saturation of the mixture with O 2. DBH is the first copper-quinoprotein hydroxylase found so far. The implications of this finding for the current views on mechanism of action and inhibition by hydrazines are discussed. The success of the recently developed ‘hydrazine method’ [(1987) FEBS Lett. 221, 299-304] for all different types of amine oxidoreductases, suggest that the method could also be applied to other enzymes for which hydrazines are inhibitors and where the identity of the cofactors has not been established or the presence of PQQ is suspected.

Reconstitution of pyrroloquinoline quinone-dependent D-glucose oxidase respiratory chain of Escherichia coli with cytochrome o oxidase

D-Glucose dehydrogenase is a pyrroloquinoline quinone-dependent primary dehydrogenase linked to the respiratory chain of a wide variety of bacteria. The enzyme exists in the membranes of Escherichia coli, mainly as an apoenzyme which can be activated by the addition of pyrroloquinoline quinone and magnesium. Thus, membrane vesicles of E. coli can oxidize D-glucose to gluconate and generate an electrochemical proton gradient in the presence of pyrroloquinoline quinone. The D-glucose oxidase-respiratory chain was reconstituted into proteoliposomes, which consisted of two proteins purified from E. coli membranes, D-glucose dehydrogenase and cytochrome o oxidase, and E. coli phospholipids containing ubiquinone 8. The electron transfer rate during D-glucose oxidation and the membrane potential generation in the reconstituted proteoliposomes were almost the same as those observed in the membrane vesicles when pyrroloquinoline quinone was added. The results demonstrate that the quinoprotein, D-glucose dehydrogenase, can reduce ubiquinone 8 directly within phospholipid bilayer and that the D-glucose oxidase system of E. coli has a relatively simple respiratory chain consisting of primary dehydrogenase, ubiquinone 8, and a terminal oxidase.

Reductive trapping of substrate to bovine plasma amine oxidase.

Plasma amine oxidases catalyze the oxidative deamination of amines to aldehydes, followed by a 2e- reduction of O2 to H2O2. Pyrroloquinoline quinone (PQQ), previously believed to be restricted to prokaryotes, has recently been proposed to be the cofactor undergoing reduction in the first half-reaction of bovine plasma amine oxidase (Ameyama, M., Hayashi, U., Matsushita, K., Shinagawa, E., and Adachi, O. (1984) Agric. Biol. Chem. 48, 561-565; Lobenstein-Verbeek, C. L., Jongejan, J. A., Frank, J., and Duine, J. A. (1984) FEBS Lett. 170, 305-309). This result is unexpected, since model studies with PQQ implicate Schiff's base formation between a reactive carbonyl and substrates, whereas experiments with bovine plasma amine oxidase have failed to provide evidence for a carbonyl cofactor. We have, therefore, re-examined putative adducts between substrate and enzyme-bound cofactor, employing a combination of [14C]benzylamine and [3H]NaCNBH3. The use of the relatively weak reductant, NaCNBH3, affords Schiff's base specificity and permits the study of enzyme below pH 7.0. As we show, enzyme can only be inactivated by NaCNBH3 in the presence of substrate, leading to the incorporation of 1 mol of [14C]benzylamine/mol of enzyme subunit at complete inactivation. By contrast, we are unable to detect any labeling with [3H]NaCNBH3, analogous to an earlier study with [3H]NaCNBH4 (Suva, R. H., and Abeles, R. H. (1978) Biochemistry 17, 3538-3545). We conclude, first, that our inability to obtain adducts containing both carbon 14 and tritium rules out the reductive trapping either of amine substrate with pyridoxal phosphate or of aldehyde product with a lysyl side chain and, second, that the observed pattern of labeling is fully consistent with the presence of PQQ at the active site of bovine plasma amine oxidase.

Energy transduction by electron transfer via a pyrrolo-quinoline quinone-dependent glucose dehydrogenase in Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter calcoaceticus (var. lwoffi).

The coupling of membrane-bound glucose dehydrogenase (EC 1.1.99.17) to the respiratory chain has been studied in whole cells, cell-free extracts, and membrane vesicles of gram-negative bacteria. Several Escherichia coli strains synthesized glucose dehydrogenase apoenzyme which could be activated by the prosthetic group pyrrolo-quinoline quinone. The synthesis of the glucose dehydrogenase apoenzyme was independent of the presence of glucose in the growth medium. Membrane vesicles of E. coli, grown on glucose or succinate, oxidized glucose to gluconate in the presence of pyrrolo-quinoline quinone. This oxidation led to the generation of a proton motive force which supplied the driving force for uptake of lactose, alanine, and glutamate. Reconstitution of glucose dehydrogenase with limiting amounts of pyrrolo-quinoline quinone allowed manipulation of the rate of electron transfer in membrane vesicles and whole cells. At saturating levels of pyrrolo-quinoline quinone, glucose was the most effective electron donor in E. coli, and glucose oxidation supported secondary transport at even higher rates than oxidation of reduced phenazine methosulfate. Apoenzyme of pyrrolo-quinoline quinone-dependent glucose dehydrogenases with similar properties as the E. coli enzyme were found in Acinetobacter calcoaceticus (var. lwoffi) grown aerobically on acetate and in Pseudomonas aeruginosa grown anaerobically on glucose and nitrate.