Description

Class I peroxidases have been found in plants, fungi, and prokaryotes. They are not glycosylated and do not have signal peptides, calcium ions, or disulfide bridges.
-Ascorbate peroxidase (APx) (EC 1.11.1.11, L-ascorbate:hydrogen-peroxide oxidoreductase): APx are found in chloroplastic organisms. They show a particularly strong specificity for the electron donor ascorbate. In higher plants, APx are separated, according to their cellular localization, into cytosolic, peroxisomal and chloroplastic.
-Catalase peroxidase (CP) (EC 1.11.1.6, hydrogen-peroxide:hydrogen-peroxide oxidoreductase): CP or HPI (hydroperoxidase I) or KatG, are mainly present in prokaryotes and marginaly in some fungi and some protists. They are fusion protein and typically have a dual catalytic activity, acting both as a catalase and as a peroxidase. In bateria, they are controlled as part of the OxyR regulon, which senses active oxygen species. the catalatic reaction of catalase-peroxidases takes place via the same two stages reaction of monofunctional catalases.
Enz (Por-Fe^III) + H₂O₂ → Cpd I (Por^+.-Fe^IV = O) + H₂O Cpd I (Por^+.-Fe^IV= O) + H₂O₂ → Enz (Por-Fe^III) + H₂O + O₂
In addition CP can use organic as electron donors for the reduction of compound I to the resting state via two one-electron transfers.
Cpd I(Por^+.-Fe^IV= O) + 2AH₂ → Enz(Por-Fe^III) + 2AH^� + H₂O
-Cytochrome C peroxidase (CcP) (EC 1.11.1.5, ferrocytochrome-c: hydrogen-peroxide oxidoreductase): CcP play a major role scavenging H₂O₂ generated during aerobic respiration from the oxidation of cytochrome c in the mitochondrial intermembrane space. CcP are abscent from non mitochondrial organisms.
-APx-CcP: hybrid sequences containing APx- and CcP-specific motifs. They have been found mainly in unicellular organisms containing mitochondria and chloroplasts.