Characterization of a carbon monoxide complex of reduced dopamine β-hydroxylase: Evidence for inequivalence of the Cu(I) centers

Ascorbate-reduced dopamine β-hydroxylase (DBH) is inhibited by CO in a competitive manner with respect to molecular O₂. Measurement of the stoichiometry of CO binding indicates 0.50 CO bound per Cu(I), which provides the first evidence that the Cu(I) centers in the reduced enzyme are structurally inequivalent. FTIR spectroscopy has been used to detect an infrared absorption band characteristic of coordinated CO, with v(CO) = 2089 cm^-1. Comparison of this frequency with those of other Cu(I)-carbonyls in both inorganic and protein systems suggests a coordination site with fewer or less basic ligands than the 3-histidine site of carbonmonoxy hemocyanin.