Characterisation of the imidazoline site on monoamine oxidase type B

Abstract: Monoamine oxidase enzymes are largely involved in the catabolism of biogenic amines. Two forms of the enzyme are socumented to exist, monoamine oxidase type A and B. The B form (MAO-B) of the enzyme has been noted to possess a high affinity site for some imidazoline ligands. This site (the I2 site) appears to exist only on a small fraction of MAO-B enzymes but the function of the site is not known. The ligands that bind to this site with high affinity appear to inhibit catalytic activity at concentrations some 1000-fold higher than those required to bind to the I2 site. The goal of the present work was to characterise the I2 site on MAO-B through radio-ligand binding and kinetic assays. In doing so, phenylethylamine was found to create a high-affinty site for 2-BFI on MAO-B. The rate of site-formation is influenced by the presence of 2-BFI. This work represents a new understanding of MAO-B kinetics and opens the door for future research into the potential importance of the I2 site on MAO-B.