The fluorescence quenching spectra of the holo-Cu A and apo-Cu A domain of cytochrome c oxidase from Para coccus versutus by KI were investigated.The results indicated that in solution part of the fluorophore tryptophanes of the Cu A domain are exposed to the surface of the protein,and others buried inside o f the hydrophobic core.The fluorescence quenching constants of holo-Cu A and apo-Cu A domain protein by KI are1.39and2.24,respectively,which suggested t hat the bi-nuclear copper center[Cu A+1.5 -Cu A+1.5 ]also plays a role on the structural stability of the protein.
