In
order to extract the heme from HRP, acidified enzyme solution was incubated with an excess
of ethyl acetate for 1 min. After centrifugation, the aqueous phase was transferred and protein
content was determined by the Bradford method. Catalysis was then carried out using
untreated (control) and heme-depleted HRP in 5 mM of guaiacol in 50 mM KPi buffer. After 5
min of plasma treatment, absorption at 470 nm was determined and normalized to protein
content of the sample as well as treatment time. The experiment was performed 3 times
independently.