The mechanism of inhibition of benzylamine oxidase by 3,5-diethoxy-4-aminomethylpyridine (B24).
B24, 3,5-diethoxy-4-aminomethylpyridine, is a specific inhibitor of the semicarbazide-sensitive amine oxidase with high affinity for benzylamine (BnNH2.SSAO). It is a site-directed inhibitor of pig plasma benzylamine oxidase (BAO) with an affinity for the enzyme much higher than that for benzylamine. B24 inhibition is dependent on the molar ratio B24/BAO because the inhibitor reacts mole to mole with the enzyme and benzylamine appears to be ineffective in removing the inhibitor from the adduct [EI]. B24 is a weak substrate of BAO and for this reason the degree of inhibition (when the molar ratio B24/BAO is lower than 1) decreases with the incubation time as well as with the preincubation time. This decrease is dependent on the gradual release of free enzyme which reacts with the substrate, giving [ES] without any interfering free B24. When the B24/BAO molar ratio is higher than 1, the free enzyme released by the oxidative deamination of B24 reacts with the substrate, but the free B24 present competitively inhibits the formation of [ES] and the affinity of benzylamine is therefore reduced. This is the reason why B24, in the kinetic experiments in which the inhibitor is not pre-incubated with the enzyme, may appear to be a competitive inhibitor or a mixed inhibitor, mainly competitive. When B24 is preincubated with the enzyme and the initial rate of benzylamine oxidation is measured, it appears as a non-competitive inhibitor becoming a mixed one only when the B24/BAO molar ratio is high and the incubation time is long.
Buffoni
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F
Department of Pharmacology, University of Florence, Firenze, Italy. buffoni@stat.ds.unifi.it
Bertini
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V
Dini
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D000447:Aldehydes / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D001595:Benzylamine Oxidase / Q000037:antagonists & inhibitors* / Q000097:blood / Q000737:chemistry*; D001596:Benzylamines / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology*; D008956:Models, Chemical; D010084:Oxidation-Reduction; D011725:Pyridines / Q000493:pharmacokinetics / Q000494:pharmacology*; D013053:Spectrophotometry; D013552:Swine
C094718:3,5-diethoxy-4-aminomethylpyridine; D000447:Aldehydes; D001596:Benzylamines; D004791:Enzyme Inhibitors; D011725:Pyridines; C030796:benzylamine; D001595:Benzylamine Oxidase