Peroxidases are proteins that contain heme and are widely active in plants, microorganisms, and animals. In this review study on plant peroxidases, in addition to introducing them, how to measure the activity of the enzyme, checking the number of isozymes, and tracking the structural changes of the enzyme have also been examined. This two-substrate enzyme, which converts hydrogen peroxide into water, oxidizes many organic and inorganic substrates during its catalysis, all of which can be used to measure enzyme activity. However, its specific substrate is still hydrogen peroxide. The presence of calcium and at least four disulfide bonds in the structure of peroxidases have been proven to help the formation and strength of the three-dimensional structure of the molecule. Peroxidases of plants have several roles, including involvement in lignin biosynthesis, auxin metabolism, cell growth, creation of transverse connections of the cell wall, and especially response to environmental stresses. It has been proven that in all physiological processes and phenological changes of the plant, hydrogen peroxide is produced in tissues, and peroxidase catalase cleans the cell from this toxic substance in two different ways. Therefore, peroxidases are considered a good option to follow the path of the cell's confrontation with stress-causing factors and to face situations such as oxidative stress. Due to the advances in biological sciences and the production of pure samples of peroxidases, this molecule is also used for ligand-protein studies in pharmaceutical research.
