Continuous spectrophotometric method for determining monophenolase and diphenolase activities of pear polyphenoloxidase.

摘要

A continuous spectrophotometric method was developed based on the coupling reaction between 3-methyl-2-benzothiazolinone hydrazone (MBTH) and the quinone product of the oxidation of p-hydroxyphenyl propionic acid (PHPPA) or 3,4-dihydroxyphenyl propionic acid (DHPPA) in the presence of polyphenol oxidase (PPO) [catechol oxidase]. The monophenolase activity of pear PPO was characterized for the first time. The solubility and stability of the adduct formed at the optimum pH (4.3) enabled the system toreach steady-state, making it possible to determine monophenolase activity with short lag periods. This, together with the value of epsilon for the MBTH-quinone adduct, makes this method more sensitive than other continuous methods for assaying monophenolase and diphenolase activities.