Partial characterization of polyphenoloxidase from a hybridized wheat (Triticum aestivum L.)

Polyphenol oxidase was extracted and partially purified from wheat leaves by a procedure that included ammonium sulfate fractionation followed by dialysis and gel filtration chromatography. These procedures led to 35.21-fold purification with 17.65% recovery. Optimum pH, temperature, and ionic strength were determined with six substrates. Some kinetic properties of the enzyme such as V max, K M, and k cat were calculated for the substrates. The k cat/K M values of the PPO for catechol, catechin, pyrogallol, l-dopa, dopamine, and 4-methyl catechol were 31408, 31167, 28404, 15378, 4865, and 4967 mM/min, respectively. The best substrate of wheat PPO was found to be catechol. The native molecular weight of the PPO was estimated to be 243 kDa based on its mobility in gel filtration column. The inhibitory effects of glutathione, sodium azide, ascorbic acid, oxalic acid, l-cysteine, and thiourea on the reaction catalyzed by the enzyme were tested, and I 50 values were estimated to be 8.0 mM, 10.12 mM, 11.18 mM, 77.33 mM, 183 mM, and 413 mM, and K i constants were also calculated as 0.416 ± 0.244 mM, 0.317 ± 0.208 mM, 0.820 ± 0.111 mM, 13.80 ± 1.179 mM, 14.10 ± 5.069 mM, and 130 ± 62.45 mM, respectively, by means of Lineweaver–Burk graphs. The most effective inhibitor was glutathione. Glutathione, sodium azide, oxalic acid, and thiourea were competitive inhibitors, whereas ascorbic acid and l-cysteine were also noncompetitive inhibitors.