The irreversible inactivation of two copper-dependent monooxygenases by sulfite: peptidylglycine α-amidating enzyme and dopamine β-monooxygenase

Peptidylglycine α-amidating enzyme (α-AE) and dopamine β-monooxygenase (DβM), two copper-dependent monooxygenases that have catalytic and structural similarities, are irreversibly inactivated by sodium sulfite in a time- and concentration-dependent manner. Studies with α-AE show that the sulfite-mediated inactivation is dependent on the presence of redox active transition metals free in solution, with Cu(II) being the most effective in supporting the inactivation reaction. Sulfite inactivation of α-AE is specific for the monooxygenase reaction of this bifunctional enzyme and amidated peptides provide protection against the inactivation. Consequently, the sulfite-mediated inactivation of α-AE and DβM most likely results from the transition metal-catalyzed oxidation of sulfite to the sulfite radical, SO3−.