The catalase dataset consists of the 20pmol of digested Bovine catalase (gi 115698). Trypsinized and carboxymethylated protein was purchased from MICHROM Bioresources. Tandem mass spec dataset was acquired via a continuous reverse phase elution off the BioBasic C18 column for 85min with the final acetonitrile concentration of 45%. The total number of acquired MS/MS scans is 2,357.