Structural and catalytic properties of copper in lysyl oxidase

The spectral and catalytic properties of the copper cofactor in highly purified bovine aortic lysyl oxidase have been examined. As isolated, various preparations of purified lysyl oxidase are associated with 5-9 loosely bound copper atoms per molecule of enzyme which are removed by dialysis against EDTA. The enzyme also contains 0.99 +/- 0.10 g atom of tightly bound copper per 32-kDa monomer which is not removed by this treatment. The copper-free apoenzyme, prepared by dialysis of lysyl oxidase against alpha,alpha'-dipyridyl in 6 M urea, catalyzed neither the oxidative turnover of amine substrates nor the anaerobic production of aldehyde at levels stoichiometric with enzyme active site content, thus contrasting with the ping pong metalloenzyme. Moreover, the spectrum of the apoenzyme was not measurably perturbed upon anaerobic incubation with n-butylamine, while difference absorption bands were generated at 250 and 308 nm in the spectrum of the metalloenzyme incubated under the same conditions. A difference absorption band also developed at 300-310 nm upon anaerobic incubation of pyrroloquinoline quinone, the putative carbonyl cofactor of lysyl oxidase, with n-butylamine. Full restoration of catalytic activity occurred upon the reconstitution of the apoenzyme with 1 g atom of copper/32-kDa monomer, whereas identical treatment of the apoenzyme with divalent salts of zinc, cobalt, iron, mercury, magnesium, or cadmium failed to restore catalytic activity. The EPR spectrum of copper in lysyl oxidase is typical of the tetragonally distorted, octahedrally coordinated Cu(II) sites observed in other amine oxidases and indicates coordination by at least three nitrogen ligands. The single copper atom in the lysyl oxidase monomer is thus essential at least for the catalytic and possibly for the structural integrity of this protein.