MONOPHENOLASE ACTIVITY OF POLYPHENOL OXIDASE FROM HAAS AVOCADO

Avocado polyphenol oxidase (PPO) has been isolated and partially purif ied by using Triton X-114, reported here for the first time. The enzym e showed both monophenolase and diphenolase activities. The monophenol ase activity of avocado PPO was characterized using 4-hydroxyanisole ( 4HA) as substrate with 3-methyl-2-benzothiazolinone hydrazone as coupl ed nucleophile. This continuous spectrophotometric method was reliable , with high sensitivity and precision. 4HA was a very good substrate f or avocado PPO, showing a higher k(cat) than that for L-dopa at the op timum pH. Monophenolase activity of PPO showed a lag period (tau) prio r to the attainment of the steady state rate (V-SS). The optimum pH wa s 5, the same for the monophenolase and diphenolase activities when th e p-hydroxyphenylpropionic acid/3,4-dihydroxyphenylpropionic acid pair was assayed, as well as when 4HA was assayed. A reaction mechanism fo r explaining the kinetic behavior of the monophenolase activity of avo cado PPO has been proposed and characterized.