Diamine oxidase from pig kidney: new purification method and amino acid composition

Aminoalkyl affinity matrices

Aminoalkyl matrices are used in affinity chromatography of amine oxidases and other proteins with affinity for amino groups. Under appropriate circumstances chromatography on aminoalkyl matrices may yield purification factors around 100 to 1000, and they have been used in affinity purification of many members of the amine oxidase family. Other proteins with affinity for aminoalkyl matrices include thiol ester proteins, lactoferrin, and proteins with lysine-binding kringles (plasminogen, plasminogen activator, apolipoprotein A). The affinity of thiol ester proteins for aminoalkyl matrices is abolished after inactivation of the thiol ester group by reaction with low molecular weight amines including ammonia. Due to this, an ammonium sulphate precipitation step should be included in purification schemes for amine oxidases. The affinity of lactoferrin for aminoalkyl matrices stems from an affinity for the repeating amino groups in glycosaminoglycans, and this explains why lactoferrin requires diamines for efficient elution. The affinity of plasminogen for aminoalkyl groups is exploited in a one-step purification from plasma, and is also utilised in purification schemes for angiostatin, an angiogenesis-inhibiting fragment of plasminogen. Apolipoprotein A is homologous to plasminogen, and also has affinity for aminohexyl columns. The common binding motif for these proteins are lysine-binding kringles. Due to the properties of the amino group itself, aminoalkyl matrices will inevitably also function as anion exchangers, and this must be taken into consideration in the choice of conditions for sample loading, column washing and elution of bound proteins. Depending on the length of the alkyl chain, the matrices also have a potential for hydrophobic interactions. This property has been exploited in the purification of several proteins but must be minimized during affinity chromatography of amine oxidases. In conclusion, aminoalkyl matrices are valuable tools for affinity chromatography of several different proteins, and simple variations of sample pretreatment, sample loading, and column washing and elution conditions allow efficient selective purification of proteins with different affinities for the matrices.

Highly efficient purification of porcine diamine oxidase

Diamine oxidase (DAO) is a member of the class of copper-containing amine oxidases and catalyzes the oxidative deamination of histamine and other biogenic amines. The enzyme from porcine kidney was purified by consecutive chromatography on concanavalin A Sepharose, heparin Sepharose and Mono Q. Besides being simpler and faster than previous methods, this new purification scheme results in a homogenous product with a considerably higher yield and allows the rapid purification of large amounts of DAO from mammalian tissues. The availability of sufficient pure protein will greatly facilitate future studies of the structure and function of the enzyme.

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.

Mechanism-based inactivation of porcine kidney diamine oxidase by 1,4-diamino-2-butene

Cis- and trans-1,4-diamino-2-butene are substrates and potent inactivators of porcine kidney diamine oxidase. Evidence from absorption and NMR spectra indicates that both are oxidized to pyrrole. Both substrates are irreversible mechanism-based inactivators of the enzyme, although the trans isomer is more potent and results in complete inactivation in a reaction which follows pseudo-first-order kinetics with an apparent Ki of 0.34 mM and a second-order inactivation constant of 500 M-1 s-1. Under the same conditions, 46% of the activity remains when the enzyme is reacted with cis-1,4-diamino-2-butene. Trans-4-amino-2-butenal, the product of oxidation of the trans diamine, has been synthesized and shown to undergo cyclization to pyrrole in a concentration-dependent manner, approaching second-order at low concentrations. Trans-4-amino-2-butenal is itself a potent irreversible inhibitor with IC50 of 2.5 microM. We propose that the irreversible inactivation by both cis- and trans-1,4-diamino-2-butene involves attack by a protein-based nucleophilic residue on the unsaturated aminoenal products of the enzymatic reactions, resulting in a covalent adduct. Cyclization of the cis-aminoenal to pyrrole is much more rapid than in the trans case, thus it is less available for inhibitory reaction with the protein.

Hydroxyl radical production in the reactions of copper-containing amine oxidases with substrates

Solutions of porcine kidney diamine oxidase, PKDAO, and bovine plasma amine oxidase, BPAO, were saturated with the spin-trapping agent alpha-phenyl-N-t-butylnitrone, PBN, and incubated with cadaverine or benzylamine substrate, respectively, under aerobic conditions. EPR spectra due to trapped hydroxyl radicals were obtained for both enzymes with no evidence of superoxide formation. Under anaerobic conditions, hydroxyl radicals were formed only when H2O2 was present as well as substrate. Catalase prevented hydroxyl radical formation by PKDAO but not BPAO. The results indicate that hydroxyl radical is produced in the reaction of the product H2O2 with the reduced enzymes and therefore may be important in turnover-related enzyme degradation, but is not a true reaction intermediate.

The amplified detection of free and bound methoxatin (PQQ) with nitroblue tetrazolium redox reactions: insights into the PQQ-locus

Porcine kidney diamine oxidase, a PQQ-enzyme, can be directly measured by formazan production with putrescine and nitroblue tetrazolium. This cyclic reaction in air is unaffected by superoxide dimutase, suggesting a two electron transfer between substrate-reduced PQQ-locus and nitroblue tetrazolium, without intermediate formation of superoxide. With albumin-bound PQQ and detergent-exposed PQQ-loci, glycine can be oxidized by PQQ and electrons repetitively transferred through PQQ-sites to nitroblue tetrazolium, the rate of formazan production detecting picomoles of exposed PQQ-locus. Exposed PQQ-loci are also reducible with NaCNBH3. Nitroblue tetrazolium, reoxidizes the reduced PQQ-locus with formazan production. These experiments suggest that the PQQ-locus of quinoproteins contains a [ketone-ketoimine in equilibrium with ketoamine] redox center.