On the active site of diamine oxidase: kinetic studies

Electrostatic compared with hydrophobic interactions between bovine serum amine oxidase and its substrates

A steady-state kinetic study of bovine serum amine oxidase activity was performed, over a wide range of pH values (5.4-10.2) and ionic strength (10-200 mM), using various (physiological and analogue) substrates as specific probes of the active-site binding region. Relatively small changes in k (cat) values (approx. one order of magnitude) accompanied by marked changes in K(m) and k(cat)/K(m) values (approx. six orders of magnitude) were observed. This behaviour was correlated with the presence of positively charged groups or apolar chains in the substrates. In particular, it was found that the docking of the physiological polyamines, i.e. spermidine and spermine, appears to be modulated by three amino acid residues of the active site, which we have named L(-)H(+), G(-)H(+) and IH(+), characterized by p K (a) values of 6.2+/-0.2 [Di Paolo, Scarpa, Corazza, Stevanato and Rigo (2002) Biophys. J. 83, 2231-2239], 8.2+/-0.3 and 7.8+/-0.4 respectively. The electrostatic interaction between the protonated substrates and the enzyme containing the residues L(-)H(+), G(-)H(+) and IH(+) in the deprotonated form, the on/off role of the IH(+) residue and the role of hydrophobic interactions with substrates characterized by apolar chains are discussed.

Purification and characterization of diamine oxidase from porcine kidney and intestine

Diamine oxidase, the enzyme catalyzing the oxidative deamination of histamine and other diamines, was purified from porcine kidney and porcine intestine. During all purification steps the enzymes from both tissues showed identical binding and elution characteristics. The native enzymes are homodimeric glycoproteins with an apparent molecular weight of 186 kDa. Under reducing conditions the subunits migrate at 104 kDa on SDS polyacrylamide gels and the deglycosylated subunits migrate at 93 kDa which corresponds to a carbohydrate content of 11%. The native and deglycosylated forms of kidney and intestinal diamine oxidase migrate to the same positions, respectively, on two-dimensional isoelectric focussing/SDS polyacrylamide gels. The sequences of the 21 N-terminal amino acids of both proteins are identical. A polyclonal antibody raised against the kidney enzyme binds equally well to diamine oxidase from both kidney and intestine, inhibits the enzymatic activity, and precipitates all diamine oxidase activity from tissue homogenates. The kidney and intestinal enzymes have identical substrate specificities, efficiently converting aliphatic diamines, histamine, and spermidine. For both enzymes the Km values for histamine, putrescine, and spermidine are 0.02 mM, 0.35 mM, and 3.3 mM, respectively. Spermine, aliphatic monoamines, and aromatic mono- and diamines are poor substrates. In conclusion, the diamine oxidase proteins from porcine kidney and intestine are very likely identical and constitute the only diamine oxidase activity present in these tissues. The structural identity implies identical functions of the proteins in these organs, namely the protection of the organism against high concentrations of diamines.

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.

Inhibition of plant and mammalian diamine oxidase by substrate analogues

Imidazoles, aliphatic substrate analogues and the natural dipeptides, carnosine and anserine, were investigated as inhibitors of diamine oxidase from the pig kidney, human pregnancy plasma and pea seedlings. Imidazole, methylimidazoles, N-acetylimidazole, histamine and N tau-methylhistamine are relatively potent inhibitors of mammalian diamine oxidase showing no influence on plant enzymes. Anserine and carnosine are inhibitors of pig kidney and pea seedling enzymes. Ki values are 2 microM and 10 microM respectively. Investigated natural derivatives of putrescine and cadaverine have no influence on diamine oxidase of different origin. In conclusion, we present some evidence to suggest that mammalian diamine oxidase, despite a high reaction rate with putrescine, is better adapted to histamine oxidation, whereas for plant enzymes the diamines are preferred substrates.

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.

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.