Comparison of coupling subsites and inhibition effects of piperidine alkaloids and aminoketones on plant amine oxidases.

In the present work we compare the binding subsites of inhibitors from a series of alkaloids and aminoketones on pea and sainfoin diamine oxidase (EC 1.4.3.6; DAO) by the graphical method. As standard competitive inhibitors we have chosen oxoanalogs of the substrates, namely, 1,4-diamino-2-butanone and 1,5-diamino-3-pentanone, which were compared with the alkaloids (+)-sedamine, (-)-norallosedamine, (-)-norsedamine, L-lobeline, cinchonine and aromatic analogs of aliphatic aminoketones such as 1-amino-3-phenyl-3-propanone and 1-amino-3-phenyl-2-propanone. In the case of pea DAO all inhibitors compete for the same subsites with 1,4-diamino-2-butanone and 1,5-diamino-3-pentanone (alpha = infinity). In the case of sainfoin enzyme they are bound to other subsites and the interaction constants (0 < alpha < 1) point to a positive attraction between these two types of inhibitors. With sainfoin DAO, 1-amino-3-phenyl-3-propanone is bound into the same subsite as 1,4-diamino-2-butanone. Cinchonine and 1-amino-3-phenyl-3-propanone are bound to two different subsites and the value of the interaction constant (1 < alpha < infinity) shows repulsion between the inhibitors.