LAUSR

A new plant peroxidase was isolated from the leaves of guinea grass (Panicum maximum) and partially purified using a biphasic polymer system (poly(ethylene glycol) - ammonium sulfate) followed by size-exclusion chromatography and ultracentrifugation until obtaining a homogeneous extract containing a high peroxidase activity. The novel peroxidase was characterized as having a specific activity of 408U/mg and a molecular weight of 30kDa. The pH for its optimum activity was 8.0 and exhibited a high thermostability at 66°C with a kinact of 8.0×10-3min-1. The best substrates for peroxidase from guinea grass are o-dianisidine and 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid). POD from guinea grass was directly immobilized on the surface of a graphene screen printed electrode and cyclic voltammograms in the presence of potassium ferrocyanide ([Fe(CN)6]3-/4-) as a redox species demonstrated an increase in the electron transfer process. The graphene- modified electrode exhibits excellent electrocatalytic activity to the reduction of H2O2, with a linear response in the 100μM to 3.5mM concentration range and a detection limit of 150μM. The new peroxidase from guinea grass allowed the modification of a graphene electrode providing a potential sensor detection system for determination of H2O2 in real samples with some biomedical or environmental importance.