title: Polyphenol oxidase from yacon roots (Smallanthus sonchifolius).
abstract: Polyphenol oxidase (E.C. 1.14.18.1) (PPO) extracted from yacon roots (Smallanthus sonchifolius) was partially purified by ammonium sulfate fractionation and separation on Sephadex G-100. The enzyme had a molecular weight of 45 490+/-3500 Da and Km values of 0.23, 1.14, 1.34, and 5.0 mM for the substrates caffeic acid, chlorogenic acid, 4-methylcatechol, and catechol, respectively. When assayed with resorcinol, DL-DOPA, pyrogallol, protocatechuic, p-coumaric, ferulic, and cinnamic acids, catechin, and quercetin, the PPO showed no activity. The optimum pH varied from 5.0 to 6.6, depending on substrate. PPO activity was inhibited by various phenolic and nonphenolic compounds. p-Coumaric and cinnamic acids showed competitive inhibition, with Ki values of 0.017 and 0.011 mM, respectively, using chlorogenic acid as substrate. Heat inactivation from 60 to 90 degrees C showed the enzyme to be relatively stable at 60-70 degrees C, with progressive inactivation when incubated at 80 and 90 degrees C. The Ea (apparent activation energy) for inactivation was 93.69 kJ mol-1. Sucrose, maltose, glucose, fructose, and trehalose at high concentrations appeared to protect yacon PPO against thermal inactivation at 75 and 80 degrees C.
authors.affiliation: Laboratório de Bioquímica de Alimentos, Departamento de Alimentos e Nutrição, FCF-Ar, UNESP-Universidade Estadual Paulista, Rodovia Araraquara-Jaú, km 01, CEP 14801-902, Araraquara, São Paulo, Brazil. nevesva@fcfar.unesp.br
authors.forename: Valdir Augusto
authors.initials: VA
authors.lastname: Neves
authors.forename: Maraiza Aparecida
authors.initials: MA
authors.lastname: da Silva
mesh_terms: D019659:Asteraceae / Q000201:enzymology*; D002241:Carbohydrates / Q000494:pharmacology; D004156:Catechol Oxidase / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D018517:Plant Roots / Q000201:enzymology*; D013379:Substrate Specificity
chemical_list: D002241:Carbohydrates; D004791:Enzyme Inhibitors; D004156:Catechol Oxidase