> 
> **Enzyme assays**
> 
> 
> *Determination of catalase specific activity*
> 
> 
> The CAT (EC 1.11.1.6) enzyme activity was measured according to Gallego et al.38 Plant samples were grinded in $\pu{0.1M}\ \ce{KH2PO4}$ buffer (pH $7.0$) and centrifuged at $\pu{4500 rpm}$ for $\pu{5 min}$ (Eppendorf AG bench centrifuge 5417 R, Hamburg, Germany). The supernatant was separated, added with $\pu{73 mM}\ \ce{H2O2}$, and measured at $\pu{240nm}$ through UV/Vis (Perkin Elmer Lambda 14 Spectrometer).
> 
> 
> 

The questions I want to ask are:

1. Why is $\ce{KH2PO4}$ used?
2. Why centrifuge it at 4500 rpm?
3. Why is $\ce{H2O2}$ added to the supernatant?