Conformational aspects of superoxide-dismutase-active copper chelates and catechols

The possible structural basis of the specific inhibitory action of cuprein on the autoxidation of catecholamine was examined. The chiroptical properties of the native enzyme were compared with both the denatured and the apoprotein and the superoxide-dismutase-active Cu(Tyr)₂. Apart from the reduction of cuprein copper to Cu(I), marked and characteristic changes in the circular dichroism (CD) spectrum from 260–400 nm in the presence of adrenaline and oxygen were seen, suggesting the formation of a ternary complex. This conformational change proved dependent on the concentration of oxygen, adrenaline, and cuprein copper and was not seen when the apoprotein or the heat-denatured enzyme was used. Blocking of the vicinal hydroxyl groups of adrenaline by borate did not significantly affect the formation of the complex. This implies an essential role of the catecholamine side chain. It was assumed that the ligands in close proximity around the copper appear to be even more important for the catalytic action than the involved copper. No such specificity was measured when Cu(Tyr)₂ was used. Removal of the adrenaline side chain altered the enzymic function of added cuprein copper signifiantly. During the autoxidation of 1,2-dihydroxybenzene, cuprein copper accelerated the oxidation, whereas Cu(Tyr)₂ was essentially inactive.