A mass spectrometric investigation of native and oxidatively inactivated chloroperoxidase

The enzyme chloroperoxidase (CPO) found in Calclariomyces fumago is able to catalyze several stereoselective oxidation reaction by using a dean oxidant, usually hydrogen peroxide (H2O2), without the need for expensive cofactor generation. CPO's lack of operational stability however, is a major limitation for its commercial use. In the present study, a capillary-LC on-line trypsin- digestion system combined with reversed-phase chromatography and mass spectrometric detection was optimized for studying the primary sequence of CPO. Samples containing native CPO, CPO treated with H2O2, and CPO oxidatively inactivated by the use of indole and H2O2 were analyzed and compared. Three oxidized peptides were found in the samples treated with H2O2. Two additional oxidized peptides were found in the CPO samples that were completely inactivated, one of which contained an oxidized cysteine residue, Cys50, which is an essential amio acid due to its function as the axial ligand to the iron in the heme - the prosthetic group in CPO. In addition, the heme group was absent in the inactivated samples but was readily detected in other samples