Spectroscopic studies of the reaction between bovine serum amine oxidase (copper-containing) and some hydrazides and hydrazines

The carbonyl cofactor of bovine serum amine oxidase, recently identified as pyrroloquinoline quinone [Ameyama, Hayashi, Matsushita, Shinagawa & Adachi (1984) Agric. Biol. Chem. 48, 561-565; Lobenstein-Verbeek, Jongejan, Frank & Duine (1984) FEBS Lett. 170, 305-309], reacts stoichiometrically and irreversibly with hydrazides of phenylacetic acid and of benzoic acid. With the phenylacetic hydrazides a reversible intermediate step was detected by competition with substrate, carbonylic reagents or phenylhydrazine, a typical inhibitor of the enzyme. All hydrazides form an intense broad band with maximum absorbance in a narrow wavelength range (350-360 nm), irrespective of the acyl group, suggesting that the transition is located on the organic cofactor. A different situation is found with some phenylhydrazines, where extended conjugation can occur between the cofactor and the phenyl pi-electron system via the azo group, as shown by the lower energy and higher intensity of the transition. In this case the transition is sensitive to substituents in the phenyl ring. The c.d. spectrum of the adducts is influenced by the type of hydrazide (derived from phenylacetic acid or benzoic acid), by pH and by NN-diethyldithiocarbamate binding to copper, probably as a result of shifts of equilibria between hydrazone-azo tautomers.