One might expect that some Catalases are better at the peroxidative reaction than others. It turns out that this is so. Catalases fall into two main classes, the HPI and HPII Catalases.
HPII Catalases catalyse just the disproportionation of H2O2 whereas HPI Catalases have both of the described activities. This still leaves the question of how HPI Catalases achieve their bifunctionality.
HPI Catalases exist as two isozymes, HPI-A and HPI-B and these sediment at slightly different densities.
I would be interested to know whether these two isozymes of HPI Catalase correspond to the two distinct functions, whether or not they are coded for by the same gene using alternative intron splicing and how the relative abundance of HPI-A and HPI-B is regulated.