The reaction mechanisms of oxidative degradation of the anaerobic radical enzyme pyruvate formatelyase (PFL) have been examined at the theoretical hybrid Hartree-Fock/density functional theory level B3-LYP. It is concluded that the most likely scenario involves Oz addition at the glycyl radical site, followed by H-. abstraction/transfer from C419 and subsequent rearrangements to generate an cr-hydroxyglycine and the sulfinyl radical R-SO., observed by EPR spectroscopy. In addition, the present model accounts for alternative fragmentations observed in wild-type PFL, and the formation and degradation of Gly-O-O-. in the absence of C419 (as observed in C419A and C419AC418A mutants).