While several theories have been proposed for the function of the C93–Y157 pair, the role of this post-translational modification remains unclear. Adjacent to the Fe site of CDO is a covalently cross-linked cysteine–tyrosine pair (C93–Y157). Cysteine dioxygenase (CDO) is a non-heme iron enzyme that catalyzes the O 2-dependent oxidation of l-cysteine ( l-Cys) to produce cysteinesulfinic acid (CSA).
