Ascorbate Peroxidase (APX) is a heme-containing, non-glycosylated enzyme that destroys harmful hydrogen peroxide via the ascorbate glutathione pathway in plants. This enzyme is considered to be an indispensable part of the electron-scavenging pathway and is involved in preventing oxidative damage in plants. Using differential display RT-PCR and 5' RACE a full length c-DNA clone was isolated, from citrus, with very high similarity at the nucleotide and amino acid level, to ascorbate peroxidases from several plant species. It is well known that APXs have highly conserved motifs like the Arg-38, Ars-71, Glu-65 and Asp-208 residues around the distal Hist-42 and proximal His-163. These residues are essential for binding the ligand heme. Additionally, Trp-179 is conserved in most APXs and is the third participant in hydrogen bonding network, together with His-163 and Asp-208. All these conserved motifs were present in the putative APX from citrus in addition of the presence of the peroxidase active site motif residues (APITLRLAWHSA) and the peroxidase heme-ligand motif (DIVVLSGGHTL). Expression analysis in E. Coli reviewed a recombinant protein of 27 Kda.
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