Cationic Sorghum Peroxidase and Its Participation in Plant Protection under Conditions of Pollution

A minor cationic peroxidase (MCP) with a relative electrophoretic mobility in PAGE (Rf) equal to 0.03 was first isolated from sorghum broom seedlings (Sorghum bicolor L. Moench). Its molecular weight, determined by size exclusion chromatography, was equal to 155 kDa. Three subunits with molecular weights of 35, 25, and 16 kDa were identified in the structure of the enzyme. The peroxidase and oxidase activities of MCP in the pH range from 2.6 to 7.0 were analyzed using 2,6-dimethoxyphenol (DMP), ammonium 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS), and ascorbic acid (ASA). The maximum values of peroxidase and oxidase activities were obtained in relation to ASA at pH 7.0 and 4.0, respectively. In this case, the specific activity of the peroxidase reaction exceeded that of the oxidase reaction by 68 times. K_M values for ABTS were 0.23 and 0.32 µmol for peroxidase and oxidase oxidation, respectively. The influence of certain metals and polycyclic aromatic hydrocarbons (PAHs) on the activity of MCP was studied. In the presence of sodium, its activity increased approximately 2.5 times, while it increased approximately eight times in the presence of anthracene. The enzyme efficiently oxidized native PAHs with ABTS as a mediator: 90% anthracene, 80% phenanthrene, 20% fluoranthene and 15% pyrene. It was found that three-ring PAHs underwent the most active transformation, the loss of which was five times greater than the loss of PAHs with four rings. Thus, the detected stimulation of activity MCP in the presence of inorganic and organic pollutants and the ability to oxidize a number of native PAHs may indicate its active participation in plant protection under polluted conditions.