ABSTRACT
The optical spectroscopic features shown by amine oxidases (AOs) during their catalytic cycle seem rather similar to intermediates observed with pyridoxal model systems. The oldest and never fully disproved hypothesis suggests that a special form of pyridoxal phosphate is the organic cofactor present in amine oxidases. Cycloserine, a known inhibitor of pyridoxal phosphate enzymes, also strongly inhibits AOs and gives spectrophotometrically observable adducts. CD experiments, however, show that the position, sign, and intensity of the component peaks are significantly modified in the copper-free AOs. The reaction of AOs with phenylhydrazine has been studied in detail since this compound behaves as an irreversible inhibitor. The visible absorption of AOs is particularly useful in order to study the kinetic reaction of these enzymes with their substrates. Despite several efforts, the nature of the chromophore responsible for the visible absorption in AOs is still uncertain.
