Kinetic characterization of the oxidation of chlorogenic acid by polyphenol oxidase and peroxidase. Characteristics of the o-quinone.
Chlorogenic acid is the major diphenol of many fruits, where it is oxidized enzymatically by polyphenol oxidase (PPO) or peroxidase (POD) to its o-quinone. In spectrophotometric studies of chlorogenic acid oxidation with a periodate ratio of [CGA]0/[IO4-]0 < 1 and [CGA]0/[IO4-]0 > 1, the o-quinone was characterized as follows: lambda(max) at 400 nm and epsilon = 2000 and 2200 M-1 cm-1 at pH 4.5 and 7.0, respectively. In studies of o-quinone generated by the oxidation of chlorogenic acid using a periodate at ratio of [CGA]0/[IO4-]0 > 1, a reaction with the remaining substrate was detected, showing rate constants of k = 2.73 +/- 0.17 M-1 s-1 and k' = 0.05 +/- 0.01 M-1 s-1 at the above pH values. A chronometric spectrophotometric method is proposed to kinetically characterize the action of the PPO or POD on the basis of measuring the time it takes for a given amount of ascorbic acid to be consumed in the reaction with the o-quinone. The kinetic constants of mushroom PPO and horseradish POD are determined.
Muñoz
J
J
GENZ: Grupo de Investigación de Enzimología, Departamento de Bioquímica y Biología Molecular-A, Facultad de Biología, Universidad de Murcia, E-30100 Espinardo, Murcia, Spain.
Garcia-Molina
F
F
Varon
R
R
Rodriguez-Lopez
J N
JN
García-Ruiz
P A
PA
García-Canovas
F
F
Tudela
J
J
D000363:Agaricales / Q000201:enzymology; D031215:Armoracia / Q000201:enzymology; D004156:Catechol Oxidase / Q000378:metabolism*; D002726:Chlorogenic Acid / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010084:Oxidation-Reduction; D010504:Periodic Acid / Q000378:metabolism; D009195:Peroxidase / Q000378:metabolism*; D011809:Quinones / Q000378:metabolism*
D011809:Quinones; D010504:Periodic Acid; D002726:Chlorogenic Acid; C009288:metaperiodate; D004156:Catechol Oxidase; D009195:Peroxidase