Irreversible inhibition of pig kidney copper-containing amine oxidase by sodium and lithium ions

Zymographic Determination of Intrinsic Specific Activity of Oxidases in the Presence of Interfering Proteins

Zymography on peroxidase-entrapped gels enables the determination of the intrinsic specific activity (ISA) of H₂O₂-producing oxidases in the presence of interfering enzymes including catalase (decomposing hydrogen peroxide). To reveal the searched oxidase, the zymography gel is incubated first in the developing solution containing the appropriate substrate of the oxidase and an oxidizable chromogen such as o-phenylenediamine (o-PDA) peroxidase substrate. The zymographic gel, after image analysis, can be restained by Coomassie Blue for molecular weights, for the whole electrophoretic pattern and for the protein concentration, thus allowing for the determination of oxidase ISA.

Recombinant human diamine oxidase activity is not inhibited by ethanol, acetaldehyde, disulfiram, diethyldithiocarbamate or cyanamide

Human diamine oxidase (hDAO, EC 1.4.3.22) is the key enzyme in the degradation of extracellular histamine. Consumption of alcohol is a known trigger of mast cell degranulation in patients with mast cell activation syndrome. Ethanol may also interfere with enzymatic histamine degradation, but reports on the effects on DAO activity are controversial. There are also conflicting reports whether disulfiram, an FDA-approved agent in the treatment of alcohol dependence, inhibits DAO. We therefore investigated the inhibitory potential of ethanol and disulfiram and their metabolites on recombinant human DAO (rhDAO) in three different assay systems. Relevant concentrations of ethanol, acetaldehyde, and acetate did not inhibit rhDAO activity in an in vitro assay system using horseradish peroxidase (HRP) -mediated luminol oxidation. The aldehyde dehydrogenase (ALDH; EC 1.2.1.3) inhibitors cyanamide and its dimer dicyanamide also had no effect on DAO activity. In one assay system, the irreversible ALDH inhibitor disulfiram and its main metabolite diethyldithiocarbamate seemed to inhibit DAO activity. However, the decreased product formation was not due to a direct block of DAO activity but resulted from inhibition of peroxidase employed in the coupled system. Our in vitro data do not support a direct blocking effect of ethanol, disulfiram, and their metabolites on DAO activity in vivo.

Enzyme Biosensors for Biomedical Applications: Strategies for Safeguarding Analytical Performances in Biological Fluids

Enzyme-based chemical biosensors are based on biological recognition. In order to operate, the enzymes must be available to catalyze a specific biochemical reaction and be stable under the normal operating conditions of the biosensor. Design of biosensors is based on knowledge about the target analyte, as well as the complexity of the matrix in which the analyte has to be quantified. This article reviews the problems resulting from the interaction of enzyme-based amperometric biosensors with complex biological matrices containing the target analyte(s). One of the most challenging disadvantages of amperometric enzyme-based biosensor detection is signal reduction from fouling agents and interference from chemicals present in the sample matrix. This article, therefore, investigates the principles of functioning of enzymatic biosensors, their analytical performance over time and the strategies used to optimize their performance. Moreover, the composition of biological fluids as a function of their interaction with biosensing will be presented.

Structural snapshots from the oxidative half-reaction of a copper amine oxidase: implications for O2 activation

The mechanism of molecular oxygen activation is the subject of controversy in the copper amine oxidase family. At their active sites, copper amine oxidases contain both a mononuclear copper ion and a protein-derived quinone cofactor. Proposals have been made for the activation of molecular oxygen via both a Cu(II)-aminoquinol catalytic intermediate and a Cu(I)-semiquinone intermediate. Using protein crystallographic freeze-trapping methods under low oxygen conditions combined with single-crystal microspectrophotometry, we have determined structures corresponding to the iminoquinone and semiquinone forms of the enzyme. Methylamine reduction at acidic or neutral pH has revealed protonated and deprotonated forms of the iminoquinone that are accompanied by a bound oxygen species that is likely hydrogen peroxide. However, methylamine reduction at pH 8.5 has revealed a copper-ligated cofactor proposed to be the semiquinone form. A copper-ligated orientation, be it the sole identity of the semiquinone or not, blocks the oxygen-binding site, suggesting that accessibility of Cu(I) may be the basis of partitioning O2 activation between the aminoquinol and Cu(I).

Synthetic polyamines as potential amine oxidase inhibitors: a preliminary study

In the last few decades, medicinal chemists have carried out extensive research on synthetic polyamines for use as anticancer drugs and multitarget-directed ligands in neurodegenerative diseases. The aim of this study was to evaluate the effect of some synthetic polyamines as inhibitors of two new potential targets, human semicarbazide-sensitive amine oxidase/vascular adhesion protein-1 (SSAO/VAP-1) and monoamine oxidases B (MAO B), enzymes involved in various multi-factorial diseases such as Alzheimer's disease. N,N'-Dibenzyl-dodecane-1,12-diamine (Bis-Bza-Diado), a newly synthesised compound, and ELP 12, a muscarinic cholinergic M(2) receptor antagonist, were found to behave as reversible and mixed non-competitive inhibitors of both amine oxidases (dissociation constants of about 100 μM). ELP 12 was found to be more selective for SSAO/VAP-1. Combining kinetic and structural approaches, the binding mode of ELP 12 to SSAO/VAP-1 was investigated. ELP 12 may bind at the entrance of the active site channel by ionic interactions with ASP446 and/or ASP180; one end of the polyamine may be accommodated inside the channel, reaching the TPQ cofactor area. The binding of ELP 12 induces rearrangement of the secondary structure of the enzyme and impedes substrate entry and/or product release and catalysis. These structural data reveal that the entrance and the first part of the SSAO/VAP-1 channel may be considered as a new target area, or a "secondary binding site", for modulators of human SSAO/VAP-1 activity. These results indicate ELP 12 and Bis-Bza-Diado as new "skeletons" for the development of novel SSAO/VAP-1 and MAO B inhibitors.

N-alkanamines as substrates to probe the hydrophobic region of bovine serum amine oxidase active site: A kinetic and spectroscopic study

Kinetic and spectroscopic studies were carried out to study the role of hydrophobic effect on the activity of bovine serum amine oxidase (BSAO). Increasing the chain length of the substrates (linear aliphatic primary monoamines), the affinity for the active site increases while the catalytic constant decreases in accordance with a relative low value of dielectric constant (about 10) estimated for the microenvironment of BSAO active site using a fluorescent probe sensitive to solvent polarity. The aliphatic chain of 1-aminononane induces a shift in the pK(a) of the product Schiff base, the hydrolysis of which appears to be a rate-determining step of the reaction. Furthermore, circular dichroism studies highlighted the "flexibility" of BSAO secondary structure that can explain the wide substrate specificity of this enzyme. These results should be useful to elucidate the substrate/inhibitor preferences of CuAOs, in particular of the human enzyme.

An important lysine residue in copper/quinone-containing amine oxidases

The interaction of xenon with copper/6-hydroxydopa (2,4,5-trihydroxyphenethylamine) quinone (TPQ) amine oxidases from the plant pulses lentil (Lens esculenta) and pea (Pisum sativum) (seedlings), the perennial Mediterranean shrub Euphorbia characias (latex), and the mammals cattle (serum) and pigs (kidney), were investigated by NMR and optical spectroscopy of the aqueous solutions of the enzymes. (129)Xe chemical shift provided evidence of xenon binding to one or more cavities of all these enzymes, and optical spectroscopy showed that under 10 atm of xenon gas, and in the absence of a substrate, the plant enzyme cofactor (TPQ), is converted into its reduced semiquinolamine radical. The kinetic parameters of the analyzed plant amine oxidases showed that the k(c) value of the xenon-treated enzymes was reduced by 40%. Moreover, whereas the measured K(m) value for oxygen and for the aromatic monoamine benzylamine was shown to be unchanged, the K(m) value for the diamine putrescine increased remarkably after the addition of xenon. Under the same experimental conditions, the TPQ of bovine serum amine oxidase maintained its oxidized form, whereas in pig kidney, the reduced aminoquinol species was formed without the radical species. Moreover the k(c) value of the xenon-treated pig enzyme in the presence of both benzylamine and cadaverine was shown to be dramatically reduced. It is proposed that the lysine residue at the active site of amine oxidase could be involved both in the formation of the reduced TPQ and in controlling catalytic activity.

Exploring molecular oxygen pathways in Hansenula polymorpha copper-containing amine oxidase

The accessibility of large substrates to buried enzymatic active sites is dependent upon the utilization of proteinaceous channels. The necessity of these channels in the case of small substrates is questionable because diffusion through the protein matrix is often assumed. Copper amine oxidases contain a buried protein-derived quinone cofactor and a mononuclear copper center that catalyze the conversion of two substrates, primary amines and molecular oxygen, to aldehydes and hydrogen peroxide, respectively. The nature of molecular oxygen migration to the active site in the enzyme from Hansenula polymorpha is explored using a combination of kinetic, x-ray crystallographic, and computational approaches. A crystal structure of H. polymorpha amine oxidase in complex with xenon gas, which serves as an experimental probe for molecular oxygen binding sites, reveals buried regions of the enzyme suitable for transient molecular oxygen occupation. Calculated O(2) free energy maps using copper amine oxidase crystal structures in the absence of xenon correspond well with later experimentally observed xenon sites in these systems, and allow the visualization of O(2) migration routes of differing probabilities within the protein matrix. Site-directed mutagenesis designed to block individual routes has little effect on overall k(cat)/K(m) (O(2)), supporting multiple dynamic pathways for molecular oxygen to reach the active site.

The effects of buffer cations on interactions between mammalian copper-containing amine oxidases and their substrates

We and others have observed that substrates for copper-containing amine oxidases cause substrate inhibition at high concentrations. Through use of a novel "pseudoquantitative" rapid equilibrium approach, kinetic analyses with human and bovine enzymes indicate that these effects are consistent with substrates binding to oxidised and reduced enzyme forms. Small cations compete with binding of substrates to oxidised and reduced enzyme, influencing both substrate turnover and substrate inhibition patterns. Cations reduce affinity of the resting bovine enzyme for spermidine, but not benzylamine, indicating that the predominant effect of cations on substrate oxidation results from binding to an anionic site outside the active site. However, binding of cations to the active site of the reduced form of both enzymes attenuates substrate inhibition with both spermidine and benzylamine. Our observations have significant practical implications for researchers assaying kinetic behaviour of these enzymes, and particularly those developing novel inhibitors of human copper-containing amine oxidases.

Properties of copper-free pig kidney amine oxidase: Role of topa quinone

Copper removal from pig kidney amine oxidase containing Cu/topaquinone (TPQ) has been obtained using CN(-) in the presence of the poor substrate p-(dimethylamino)benzylamine. Upon removal of copper, the enzyme loses its activity while the TPQ cofactor remains in its oxidized form. The addition of copper to the apo-form fully restores the active enzyme. The CN(-) treatment in the presence of sodium dithionite or good substrates (cadaverine or benzylamine) also removes copper but the TPQ cofactor is irreversibly reduced and the addition of copper does not regenerate the active enzyme. Ni(II) and Zn(II) do not bind the apo-protein in contrast to Co(II) which is incorporated to the same extent as Cu(II). However, Co-reconstituted enzyme only shows a very low activity. These results demonstrate that copper is essential for the catalytic mechanism because it maintains the correct active site geometry.

Cu and Cd effects on the earthworm Lumbricus rubellus in the laboratory: multivariate statistical analysis of relationships between exposure, biomarkers, and ecologically relevant parameters

This study sets out to examine the potential of a suite of novel molecular biomarkers as early warning indicators of environmental state and damage. Transcriptional responses of four genes, metallothionein 1 and 2, amine oxidase, and the lysosomal associated glycoprotein, were measured in the earthworm Lumbricus rubellus exposed to increasing concentrations of cadmium and copper in OECD soil. These responses were compared to metal body concentrations and lifecycle parameters: survival, cocoon production, and growth. Adverse physiological effects were observed at concentrations 1/3rd to 1/10th those of the artificial soil LC50. Multivariate statistics, principal component analysis (PCA), was used to investigate the correlations between the different variables. Three key components were derived explaining 77.6% of the variance, with component 1 contributing 32.4%, component 2 contributing 26.7%, and component 3 contributing 18.5%. These components were interpreted in terms of population health, pollutant exposure, and detoxification pathways, respectively. It is proposed that the use of such a suite of biomarkers could serve as indicators of the "health" of the soil environment and provide early warning signals of potential danger to the biota or as a means of monitoring soil remediation.

Binding of cations of group IA and IIA to bovine serum amine oxidase: effect on the activity

In this paper, we report on the presence of cation binding areas on bovine serum amine oxidase, where metal ions of the groups IA and IIA, such as Na(+), K(+), Cs(+), Mg(2+), and Ca(2+), bind with various affinities. We found a cation-binding area that influences the enzyme activity if occupied, so that the catalytic reaction may be altered by some physiologically relevant cations, such as Ca(2+) and K(+). This binding area appears to be localized inside the enzyme active site, because some of these cations act as competitive inhibitors when highly charged amines, such as spermine and spermidine, are used as substrates. In particular, dissociation constant values (K(d)) of 23 and 27 mM were measured for Cs(+) and Ca(2+), respectively, using, as substrate, spermine, a polyamine of plasma. An additional cation-binding area, where metal ions such as Cs(+) (K(d) congruent with 0.1 mM) and Na(+) (K(d) congruent with 54 mM) bind without affecting the enzyme activity, was found by NMR.

Structure and nucleotide sequence of Euphorbia characias copper/TPQ-containing amine oxidase gene

A cDNA encoding for a copper containing amine oxidase has been isolated and sequenced from young leaves of Euphorbia characias, a perennial mediterranean shrub. A single long open reading frame of 2068 pb encodes a protein composed of 653 amino acids with a molecular mass of about 74 kDa. A putative 24-aminoacid signal peptide precedes the sequence of the mature protein, with characteristics of a secretion signal peptide. Alignments of Euphorbia amine oxidase cDNA nucleotide sequence with that of amine oxidase from the seedlings of the pulses lentil, pea, and chickpea reveal several conserved regions, especially in the C-terminus, with a homology 90%-97%. The near 5' region shows several insertions, deletions, and different nucleotide sequence with ca. 60% homology. The enzyme contains 1%-2% carbohydrate deduced by deglycosylation experiments. Five cysteine residues are present in the deduced aminoacid sequence with a single disulfide bridge as judged by titration with cysteine reagents.

Culture medium enhances semicarbazide-sensitive amine oxidase activity

Components of fetal calf serum (FCS) are known to contribute to growth and maintenance of cultured cells. Fetal calf serum supplementation of media also may contribute to the cytotoxicity of other substances to cells grown in vitro. Semicarbazide-sensitive amine oxidase (SSAO) enzyme, present in FCS, metabolizes primary amines and contributes to amine cytotoxicity in vascular smooth muscle cells (VSMC). In cell culture experiments, the media used may greatly affect enzymic activities such as SSAO. In these studies, the SSAO activity in FCS, cultured rat aortic VSMC, and rat plasma was determined in the presence and absence of various culture media. Semicarbazide-sensitive amine oxidase activity in FCS (5-20 microl) was significantly enhanced (approximately 1.5- to 2-fold) in the presence of various culture media, with Dulbecco modified Eagle medium (DMEM), causing the greatest enhancement. Dulbecco modified Eagle medium enhanced the SSAO activity of cultured VSMC in two of the four passages but reduced activity in two passages. Activity in rat plasma was reduced by approximately 25% in the presence of DMEM. The concentrations of various media components, such as glucose, sodium pyruvate, pyridoxine.HCl, and L-glutamine, were not correlated with enhancement. This study identifies an important enhancement effect of culture media on the FCS enzyme, SSAO, although the media components responsible for the enhancement are yet to be identified.