Inhibition of plant amine oxidases by a novel series of diamine derivatives

A series of N,N′-bis(2-pyridinylmethyl)diamines was synthesized and characterized for their inhibition effects towards plant copper-containing amine oxidase (EC 1.4.3.6) and polyamine oxidase (EC 1.5.3.11), which mediate the catabolic regulation of cellular polyamines. Even though these enzymes catalyze related reactions and, among others, act upon two common substrates (spermidine and spermine), their molecular and kinetic properties are different. They also show a different spectrum of inhibitors. It is therefore of interest to look for compounds providing a dual inhibition (i.e. inhibiting both enzymes with the same inhibition potency), which would be useful in physiological studies involving modulations of polyamine catabolism. The synthesized diamine derivatives comprised from two to eight carbon atoms in the alkyl spacer chain. Kinetic measurements with pea (Pisum sativum) diamine oxidase and oat (Avena sativa) polyamine oxidase demonstrated reversible binding of the compounds at the active sites of the enzymes as they were almost exclusively competitive inhibitors with Ki values ranging from 10−5 to 10−3 M. In case of oat polyamine oxidase, the Ki values were significantly influenced by the number of methylene groups in the inhibitor molecule. The measured inhibition data are discussed with respect to enzyme structure. For that reason, the oat enzyme was analyzed by de novo peptide sequencing using mass spectrometry and shown to be homologous to polyamine oxidases from barley (isoform 1) and maize. We conclude that some of the studied N,N′-bis(2-pyridinylmethyl)diamines might have a potential to be starting structures in design of metabolic modulators targeted to both types of amine oxidases.