N-alkanamines as substrates to probe the hydrophobic region of bovine serum amine oxidase active site: A kinetic and spectroscopic study

Kinetic and spectroscopic studies were carried out to study the role of hydrophobic effect on the activity of bovine serum amine oxidase (BSAO). Increasing the chain length of the substrates (linear aliphatic primary monoamines), the affinity for the active site increases while the catalytic constant decreases in accordance with a relative low value of dielectric constant (about 10) estimated for the microenvironment of BSAO active site using a fluorescent probe sensitive to solvent polarity. The aliphatic chain of 1-aminononane induces a shift in the pKa of the product Schiff base, the hydrolysis of which appears to be a rate-determining step of the reaction. Furthermore, circular dichroism studies highlighted the ‘‘flexibility’’ of BSAO secondary structure that can explain the wide substrate specificity of this enzyme. These results should be useful to elucidate the substrate/inhibitor preferences of CuAOs, in particular of the human enzyme.