Properties of diphenolase from Vanilla planifolia (Andr.) shoot primordia cultured in vitro.

Properties of diphenolase (PPO, EC1.10.3.1) from vanilla (Vanilla planifolia Andr.) shoot primordia culture were investigated. Two pH optima of the enzyme extraction at pH 6 and 8 were found. Nevertheless, the enzymes shared the same optimum pH of activity-between pH 3 and 4. Sodium dodecyl sulfate slightly improved diphenolase extraction but caused a 3-fold increase in its specific activity. The extracts of pH 6 and 8.0 revealed three isozyme bands after polyacrylamide gel electrophoresis-two of them were similar in both extracts and two distinct. The enzyme showed high thermal stability-no loss was observed after 120 min at 50 degrees C. Diethyldithiocarbamic acid, ethylenediaminetetracetic acid disodium salt, ethylene glycol bis(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid, L-ascorbic acid, dithiothreitol, glutathione (reduced), and beta-mercaptoethanol were found to be potent inhibitors of the diphenolase studied. The enzyme showed also monophenolase activity. Km and Vmax were calculated with monophenols [p-coumaric acid, 3-(p-hydroxyphenyl)propionic acid, 4-hydroxybenzyl alcohol, 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid] and with diphenols (caffeic acid, hydrocaffeic acid, chlorogenic acid, 4-methylcatechol, protocatechuic aldehyde and acid, and 3,4-dihydroxyphenylalanine). The highest Vmax was found with 4-hydroxybenzyl alcohol and the greatest affinity to protocatechuic acid, respectively-the most abundant monophenol and one of the least abundant o-diphenols in the studied Vanilla tissue.