The metal function in the reactions of bovine serum amine oxidase with substrates and hydrazine inhibitors

Bovine serum amine oxidase (BSAO) reacts with 2-hydrazinopyridine, which bi nds the organic co-factor 2,4,5-trihydroxyphenylalanine quinone, forming a band at 435 nm. The band shifts to 526 nm around 60 degrees C, to 415 nm up on denaturation, but only shifts to 429 nm upon Cu2+ depletion. Its wavelen gth and intensity suggest that the adduct has the azo conformation, whilst the same adduct of crystalline Escherichia coli amine oxidase (ECAO) shows the hydrazone conformation in the X-ray structure.. The steady state kineti cs of aminomethyl- and aminoethylpyridines confirm that the formation of th e product Schiff base, analogous to the azo form of the 2-hydrazinopyridine adduct, is not hindered in solution. The structural stability of the adduc t in the absence of Cu2+ is taken to imply hydrogen bonding of the pyridyl nitrogen to a conserved aspartate, as in the ECAO adduct. Thus the ECAO add uct provides a good model for a transient intermediate leading to formation of the BSAO azo adduct. On the basis of this model and of the catalytic co mpetence of Co2+-substituted BSAO, confirmed by the present data, a catalyt ic reaction scheme is proposed.