Pyridoxal phosphate as a prosthetic group of pig kidney diamine oxidase

Vegetal diamine oxidase alleviates histamine-induced contraction of colonic muscles

Excess of histamine in gut lumen generates a pronounced gastrointestinal discomfort, which may include diarrhea and peristalsis dysfunctions. Deleterious effects of histamine can be alleviated with antihistamine drugs targeting histamine receptors. However, many antihistamine agents come with various undesirable side effects. Vegetal diamine oxidase (vDAO) might be a relevant alternative owing to its histaminase activity. Mammalian intestinal mucosa contains an endogenous DAO, yet possessing lower activity compared to that of vDAO preparation. Moreover, in several pathological conditions such as inflammatory bowel disease and irritable bowel syndrome, this endogenous DAO enzyme can be lost or inactivated. Here, we tested the therapeutic potential of vDAO by focusing on the well-known effect of histamine on gut motility. Using ex vivo and in vitro assays, we found that vDAO is more potent than commercial anti-histamine drugs at inhibiting histamine-induced contraction of murine distal colon muscles. We also identified pyridoxal 5′-phosphate (the biologically active form of vitamin B6) as an effective enhancer of vDAO antispasmodic activity. Furthermore, we discovered that rectally administered vDAO can be retained on gut mucosa and remain active. These observations make administration of vDAO in the gut lumen a valid alternative treatment for histamine-induced intestinal dysfunctions.

Is the catalytic mechanism of bacteria, plant, and mammal copper-TPQ amine oxidases identical?

This short review is mostly concerned with the work carried out in Rome on the copper amine oxidase from bovine serum (BSAO). The first target was the copper oxidation state and its relationship with the organic cofactor. It was found that copper is not reduced on reaction with amines under anaerobic conditions or along the catalytic cycle and that it is not within bonding distance of the quinone cofactor. The copper stability in the oxidised state was supported by BSAO ability to oxidise benzylhydrazine, a slow substrate, in the presence of N,N-diethyldithiocarbamate (DDC) and by the substantial catalytic activity of Co(2+)-substituted BSAO. Parallel work established that only one subunit of the dimeric enzyme readily binds reagents of the carbonyl group. Flexible hydrazides with a long aromatic tail were found to be highly specific inhibitors, suggesting the presence of an extended hydrophobic region at the catalytic site. A study by stopped-flow transient spectroscopy and steady state kinetics led to the formulation of a simplified, yet complete and consistent, catalytic mechanism for BSAO that was compared with that available for lentil seedling amine oxidase (LSAO). As in other copper amine oxidases, BSAO is inactivated by H(2)O(2) produced in the catalytic reaction, while the cofactor is stabilised in its reduced state. A conserved tyrosine hydrogen-bonded to the cofactor might be oxidised.

Purification and properties of diamine oxidase from Euphorbia latex

A diamine oxidase has been purified to homogeneity from the latex of an herbaceous shrub, Euphorbia characias. This enzyme has a relative molecular mass of 144,000 and is composed of two identical subunits. It contain two Cu(II) and two carbonyl-like groups per dimer. The purified enzyme is pink and shows a broad absorption in the visible region centered at 480 nm, which is modified by the addition of phenylhydrazine or semicarbazide. The electron paramagnetic resonance spectrum is typical of copper(II) in a tetragonal symmetry. This enzyme oxidizes putrescine and cadaverine at fairly high rate and, less efficiently a few related compounds, but not histamine, spermine or spermidine.

Putrescine metabolism and the study of diamine oxidase activity in vivo

The catabolism of 14C-putrescine (1,4-tetramethylene-diamine) to labeled CO2 in small laboratory animals has been studied extensively in order to establish the influence of nutritional, endocrine and other factors on this process. Special attention has been paid to treatments that are known to affect the activity of diamine oxidase (DAO, histaminase, EC, 1.4.3.6), a copper-containing enzyme characteristically inhibited by semicarbazide. Thus, copper-deficient rats metabolize putrescine more slowly than their controls. Antimalarial drugs that inhibit histamine N-methyltransferase also inhibit putrescine catabolism in vivo and DAO activity in vitro. Adrenalectomized rats metabolize the diamine at a reduced rate, a result consistent with the previously demonstrated decrease of DAO in the tissues of several species of animal. There is no effect on the rate of catabolism of putrescine when thyroid state is altered. Heparin (up to 15,000 U/kg), which releases DAO from the small (0.1 mg/kg), intestine, and aminoguanidine (0.1 mg/kg), which inhibits the enzyme powerfully, both cause decreased rates of catabolism of the diamine in rats. The putrescine-catabolizing ability returns with a half-time of recovery of 15-18 h, corresponding to the estimates of SHAFF and BEAVEN [36] for recovery of intestinal DAO activity following administration of heparin or cycloheximide. Together with out other results this suggests that what is being measured by putrescine catabolism depends to a significant extent on the activity of DAO in vitro.

Cryoenzymology and spectrophotometry of pea seedling diamine oxidase

Diamine oxidase follows bi-ter ping-pong kinetics, with an intermediate, "reduced" free-enzyme form being generated after the anaerobic conversion of amine to aldehyde. Visible spectra of diamine oxidase reacting at subzero temperatures provide evidence that this intermediate enzyme form is obtained via several other intermediates and that the environment of the Cu(II) changes dramatically during the course of the reaction [even though it is not reduced to Cu(I) during the catalytic cycle]. The spectrum of this form of diamine oxidase, which is obtained 0.5--2 h after the addition of amine at -5 to -15 degrees C, is independent of substrate, is identical with that obtained by anaerobic addition of substrate at room temperature, and provides evidence for a direct interaction of Cu(II) with the organic cofactor of the enzyme. This interaction is apparently charge transfer in nature. Upon removal of Cu(II) from the native enzyme, one obtains spectral evidence that the organic cofactor is still present. However, removal of the Cu(II) from the reduced (intermediate) enzyme form yields a featureless enzyme spectrum and a Cu(II)--chelate complex which contains a new ligand, which is presumably the second prosthetic group.

Inhibition of diamine oxidase by antihistaminic agents and related drugs

Various drugs were tested as inhibitors of diamine oxidase on the basis of chemical relationships to the enzyme substrates. It was found that serotonine tryptamine and phenformin are good competitive inhibitors while cimetidine and pheniprazine are non-competitive inhibitors. Other antihistaminic drugs like promethazine are less powerful inhibitors.

Purification and properties of human amniotic fluid diamine oxidase

Diamine oxidase (DAO) was purified from amniotic fluid. The activity was separated in two DAO fractions with pI values of 5.8 and 4.0. Molecular weight were found to be 245,000 and 485,000, respectively, with subunit molecular weight of 110,000. This indicated that they probably are dimer and tetramer of the same DAO subunit. The enzyme was active against putrescine and histamine and was strongly inhibited by carbonyl group reagents. A Ping Pong Bi Ter enzyme reaction mechanism is probable. The diamine, with one amino group protonized, is suggested to be responsible for interaction with the enzyme.

On the nature of chromophore in pig kidney diamine oxidase

The nature of the 500-nm chromophore in pig kidney diamine oxidase was investigated by absorption spectroscopy and fluorescence in the presence of various chelating or carbonyl-specific reagents. From the spectroscopic measurements the following conclusions can be drawn. First, the 500-nm absorption band is not due to copper, the reduction of which is not related to the disappearance of this band. Second, phenylhydrazine and cycloserine give rise, upon reaction with the enzyme, to absorptions very similar to those of a pyridoxal enzyme, aspartate aminotransferase. Third, these enzyme derivatives are unexpectedly non-fluorescent. Copper removal, obtained after prolonged incubation of cycloserine-treated enzyme in the presence of reducing and chelating agents, leads to a fluorescence similar to that of cycloserine-aspartate transminase. It is proposed that copper is coordinated to the postulated pyridoxal phosphate of diamine oxidase through the pyridine nitrogen.

Kinetic isotope effects on the catalytic activity of pig-plasma benzylamine oxidase

1. Isotope effects on the catalytic activity of benzylamine oxidase at pH 7 and 9 have been studied by steady-state and transient-state kinetics methods, using [alpha,alpha-2H]benzylamine as the substrate. 2. Replacement of the alpha-hydrogen atoms in benzylamine by deuterium has no significant effect on substrate-binding to benzylamine oxidase, neither does it affect the rate of reoxidation of the reduced form of the enzyme. Conversion of the primarily formed enzyme-substrate complex into the reduced enzyme species, however, exhibits an isotope effect of about 3. 3. The data obtained are consistent with a mechanism in which reduction of benzylamine oxidase takes place by a rapid pre-equilibration between enzyme and substrate to form an amine-pyridoxal Schiff-base, which is then tautomerized by a comparatively slow prototropic shift to an amino aldehyde-pyridoxamine Schiff-base from which there is a rapid hydrolytic release of the aldehyde product corresponding to the amine substrate. Proton abstraction from the alpha-carbon of the amine moiety in the primary Schiff-base appears to be at least partially rate-limiting for the tautomerization step, and hence for the entire process of enzyme reduction.

Time-dependent inhibition of diamine oxidase by carbonyl-group reagents and urea

1. The behaviour of several carbonyl group reagents and urea as time-dependent inhibitors of both pig kidney and human placental diamine oxidase is described. 2. Plots of log (vt/vo) against time were not linear with these reagents as the usual theories predict. 3. This was particularly the case with aminoguanidine and phenylhydrazine and a thorough study of the effects of these compounds on the human placental diamine oxidase is described. 4. By applying a new theory for time-dependent inhibition, the inhibition of diamine oxidase by aminoguanidine and phenylhydrazine is adequately accounted for. 5. The time-dependent recovery of activity on addition of sodium pyruvate suggested that the compounds used are acting solely as carbonyl group reagents, inhibiting by Schiff-base formation at the active-site carbonyl group.

Kinetics of the diamine oxidase reaction

1. The oxidation of p-dimethylaminomethylbenzylamine was followed spectrophotometrically by measuring the change in E(250) caused by the p-dimethylaminomethylbenzaldehyde produced under a wide variety of experimental conditions. 2. The effect of variations in concentrations of both substrates (amine and oxygen) and all products (aminoaldehyde, hydrogen peroxide and ammonia) on this reaction was studied and the results used to develop a formal mechanism. 3. The nature of the rate-limiting step was elucidated by studying the effects of alterations in ionic strength, dielectric constant and deuterium substitution on the velocity of the forward reaction. 4. Thermodynamic activation energy parameters were obtained at several pH values from the effects of temperature on the reaction.

Inhibition of pig kidney diamine oxidase by substrate analogues

1. The oxidation of p-dimethylaminomethylbenzylamine was followed spectrophotometrically by measuring the change in E(250) caused by the p-dimethylaminomethylbenzaldehyde produced. 2. This reaction was inhibited by substrate analogues such as isothiouronium, guanidino, dimethylsulphonium and trimethylammonium compounds. 3. The inhibition by both mono- and bis-onium compounds has been studied and a comprehensive theory is developed to explain both the type and degree of inhibition produced.

Microbial oxidation of amines. Spectral and kinetic properties of the primary amine dehydrogenase of Pseudomonas AM1

1. An improved procedure is reported for purification of the amine dehydrogenase from methylamine-grown Pseudomonas AM1 which yielded a product homogeneous by sedimentation and disc-electrophoretic analysis, with molecular weight of 133000. 2. The purified enzyme had absorption maxima at 280 and 430nm. On aging, a third peak appeared at 325nm, and the 430nm peak decreased in intensity. This spectrum was independent of pH. 3. Addition of 2.5mm-semicarbazide, phenylhydrazine, hydrazine or hydroxylamine produced modified spectra with maxima respectively at 400, 440, 395 and 425nm. 4. Aerobic addition of methylamine resulted in a bleaching of the 430nm peak and the appearance of a new one at 325nm. This spectral change was retained after removal of the methylamine by dialysis. The original spectrum could be restored on addition of phenazine methosulphate. 5. Addition of borohydride partially inactivated the enzyme and produced spectral changes similar to those observed with methylamine. Pre-treatment with methylamine prevented the inactivation by borohydride. The degree of inactivation could be increased by alternate phenazine methosulphate and borohydride treatments. 6. The addition of methylamine or borohydride each caused shifts in the fluorescence emission maximum from 348 to 380nm. 7. Lineweaver-Burk plots of reciprocal activity against reciprocal concentration of either of the substrates n-butylamine or phenazine methosulphate were consistent with a mechanism that involves interconversion of two free forms of the enzyme by the two substrates. 8. The enzyme, although spectrally modified, was not inactivated by dialysis against diethyldithiocarbamate, and contained about 0.27 g-atom of copper/mol, with small traces of cobalt, iron and zinc. 9. Conventional methods of resolution did not release the prosthetic group. Heat denaturation after treatment of the enzyme with methylamine liberated a yellow chromophore which did not reactivate resolved aspartate aminotransferase, and whose spectral, electrophoretic and fluorescence properties did not agree with any recognizable pyridoxal derivatives. 10. Despite the inconclusive results with the isolated chromophore, the observations on the enzyme suggest that it may contain a pyridoxal derivative bound as a Schiff's base which is converted into the pyridoxamine form on aerobic treatment with methylamine and reconverted into the pyridoxal form with phenazine methosulphate. 11. The copper detected is probably not involved in the enzyme mechanism, since most copper-chelating agents are not inhibitory, and since the enzyme does not react with oxygen.

A rat liver system that catalyses a pyridoxal phosphate-independent alpha beta-eliminto

1. Attempts were made to demonstrate the presence of pyridoxal phosphate in the rat liver system catalysing the alphabeta-elimination of l-serine O-sulphate. 2. Methods designed to resolve protein-bound cofactor, spectroscopic examination of a purified enzyme system and attempted reactivation of apo-(alanine aminotransferase) failed to demonstrate the presence of pyridoxal phosphate. 3. The activity of the alphabeta-eliminating system remained constant in vitamin B(6)-deficient animals even though the activities of other pyridoxal phosphate-dependent systems fell markedly. 4. The metabolism of l-serine O[(35)S]-sulphate in vivo appears to be normal in vitamin B(6)-deficient animals. 5. No incorporation of tritium into the alphabeta-eliminating system occurred after administration of tritiated pyridoxine to experimental animals.

Purification and properties of an amine dehydrogenase from Pseudomonas AM1 and its role in growth on methylamine

1. Whole cells of Pseudomonas AM1 grown on methylamine oxidize methylamine, formaldehyde and formate. Crude extracts oxidize methylamine only if supplemented with phenazine methosulphate. 2. By using a spectrophotometric assay, the methylamine-oxidizing enzyme has been purified 20-fold in 31% yield. 3. The enzyme is a dehydrogenase, unable to utilize oxygen, NAD, NADP, flavines or menadione as electron acceptors, but able to utilize phenazine methosulphate, ferricyanide, cytochrome c or brilliant cresyl blue. 4. The enzyme is non-specific, readily oxidizing aliphatic monoamines and diamines, histamine and ethanol-amine. Secondary and tertiary amines, quaternary ammonium salts and aromatic amines are not oxidized. 5. The pH optima for methylamine, n-pentylamine and putrescine are respectively 7.6, 8.0 and 8.5. 6. The K(m) value for methylamine is 5.2mum and that for phenazine methosulphate 56mum. 7. The enzyme will withstand heating for 15min. at 80 degrees without loss of activity, but is inactivated at higher temperatures. It is not inactivated by any pH value between 2.6 and 10.6. 8. The dehydrogenase is inhibited by semicarbazide (K(i) 3.35mum), isoniazid (K(i) 1.17mum), cuprizone (K(i) 0.49mum), p-chloromercuribenzoate (K(i) 0.45mm) and quinacrine (K(i) 12.1mm). 9. The enzyme is absent from succinate-grown cells, and, during adaptation from succinate to methylamine, activity appears before growth on methylamine begins.