Some biochemical properties of polyphenol oxidase from celery.
Polyphenol oxidase (PPO, EC 1.14.18.1) was extracted from celery roots (Apium graveolens L.) with 0.1 M phosphate buffer, pH 7.0. The PPO was partially purified by (NH4)2SO4 and dialysis. Substrate specificity experiments were carried out with catechol, pyrogallol, L-DOPA, p-cresol, resorcinol, and tyrosine. The Km for pyrogallol, catechol, and L-DOPA were 4.5, 8.3, and 6.2mM, respectively, at 25 degrees C. Data for Vmax/Km values, which represent catalytic efficiency, show that pyrogallol has the highest value. The optimum pH and temperature were determined with catechol, pyrogallol, and L-DOPA. Optimum pH was 7.0 for catechol and L-DOPA, and 7.5 for pyrogallol. Optimum temperatures for maximum PPO activity were 25 degrees C for pyrogallol, 40 degrees C for catechol, and 45 degrees C for L-DOPA. Heat inactivation studies showed a decrease in enzymatic activity at temperatures above 60 degrees C. The order of inhibitor effectiveness was: L-cysteine > ascorbic acid > glycine > resorcinol > NaCl.
Yagar
Hülya
H
Department of Chemistry, Trakya University, Edirne, Turkey. hulyagar@yahoo.com
D000077102:Apium / Q000201:enzymology*; D004156:Catechol Oxidase / Q000032:analysis* / Q000037:antagonists & inhibitors / Q000737:chemistry*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000737:chemistry; D004795:Enzyme Stability; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008970:Molecular Weight; D018517:Plant Roots / Q000201:enzymology*; D013379:Substrate Specificity; D013696:Temperature
D004791:Enzyme Inhibitors; D004156:Catechol Oxidase