Reduced anion binding and anion inhibition in Cu, Zn superoxide dismutase chemically modified at lysines without alteration of the rhombic distortion of the copper site

The spectroscopic binding constant (visible absorption and EPR spectra) and the catalytic inhibition constant of N3− and CN− were measured for bovine Cu, Zn superoxide dismutase chemically modified at all lysines by either succinylation or carbamoylation. These modifications partially inactivate the enzyme (10% and 50% residual activity respectively) but leave the native rhombic geometry of the copper site unaffected. It could thus be shown that the observed reduction of anion affinity of the lysines-modified proteins is related to the decreased positive charge of the protein.