B. Bertocci

Binding of [3H]dihydrotetrabenazine and [125I]azidoiodoketanserin photoaffinity labeling of the monoamine transporter of platelet 5-HT organelles.

The carrier for 5-hydroxytryptamine (5-HT) of the 5-HT storage organelles of blood platelets was characterized by [3H]dihydrotetrabenazine binding and [125I]azidoiodokentanserin photoaffinity labeling. [3H]Dihydrotetrabenazine bound with high affinity to membrane preparations from different animal species. The [3H]dihydrotetrabenazine Bmax value was about 10-fold higher in rabbit (9.4 +/- 1.3 pmol/mg protein) than in human, rat and guinea-pig preparations (Bmax values = 1.1 +/- 0.2, 1.2 +/- 0.1 and 0.52 +/- 0.06 pmol/mg protein, respectively). After rabbit platelet subcellular fractionation, [3H]dihydrotetrabenazine binding was highly enriched in the fraction corresponding to pure 5-HT organelles, whereas ligand binding was much lower in the other subcellular fractions. Conversely, [3H]paroxetine binding sites were more concentrated in the lower density fractions, with no binding to the 5-HT granules. In competition experiments, [3H]dihydrotetrabenazine binding to human platelet membranes and rabbit platelet 5-HT organelles was markedly inhibited by the benzo[a]quinolizine derivatives, tetrabenazine and Ro 4-1284, and by ketanserin. In isolated rabbit platelet 5-HT organelles, reserpine showed a relatively high IC50 (930 nM), but the presence of ATP increased its potency about 10-fold. Paroxetine, methysergide and carrier substrates had little or no effect. After photoaffinity labeling of rabbit 5-HT granules with [125I]azidoiodoketanserin, the radioactivity was incorporated into several polypeptides. The presence of Ro 4-1284, reserpine and ketanserin prevented the labeling of a polypeptide of 85 kDa. The data obtained suggest that this protein represents a component of the granular carrier which binds [3H]dihydrotetrabenazine.

Reaction of pig plasma benzylamine oxidase with betaaminopropionitrile

Beta-aminopropionitrile (BAPN) is an inhibitor of pig plasma benzylamine oxidase. BAPN is oxidized by benzylamine oxidase. Inhibition develops in a time-dependent fashion upon incubation of BAPN with the enzyme in the absence of substrate. The product of oxidation of BAPN by benzylamine oxidase, cyanacetaldehyde, was identified and prepared by synthesis. It is an irreversible inhibitor of the enzyme.

Effect of Pyridoxamine on Semicarbazide‐sensitive Amine Oxidase Activity of Rabbit Lung and Heart

Abstract— Rabbit lung and heart show clorgyline‐resistant benzylamine oxidase activity which is sensitive to semicarbazide (SSAO) and α‐amino‐guanidine. This SSAO activity is inhibited by pyridoxamine with an IC50 of 6·3 × −6 M for lung and of 1·1 × 10−5 M for heart, the inhibition being non‐competitive and only partially reversed by dialysis at 4°C. Semicarbazide, α‐aminoguanidine and pyridoxamine show a similar time‐dependent type of inhibition of rabbit lung and heart SSAO.

Guanabenz as inhibitor of copper-containing amine oxidases

The effects of guanabenz on some copper containing amine oxidases are described. Guanabenz ‘in vitro’ inhibits pig plasma benzylamine oxidase with a IC50M 5.1±0.8×10−6M. It also inhibits pig kidney diamine oxidase and rat liver mitochondrial monoamine oxidase at higher concentrations. The significance of this property of guanabenz is discussed.

Monoclonal antibodies recognizing both soluble and membrane bound catechol-O-methyltransferase

Both cytosolic, soluble and membrane-bound catechol-O-methyl-transferase (COMT) from pig and rat liver or kidney were recognized by mouse monoclonal antibodies (MAbs) raised against soluble COMT isolated from pig liver. In ELISA, the MAbs Co 16 and Co 54 reacted better with the pig than with the rat enzyme. The MAb Co 60 showed good reactivity with both pig and rat COMT. In addition, all three MAbs recognize the soluble (23 kDa) as well as the membrane-bound (26 kDa) forms of the COMT enzyme.