PURIFICATION AND CHARACTERIZATION OF TOMATO LEAF (LYCOPERSICON-ESCULENTUM MILL.) HYDROPEROXIDE LYASE

Hydroperoxide lyase (HPOOH lyase) was extracted from tomato leaves (Ly copersicon, esculentum Mill.) and purified to apparent homogeneity by fractionated precipitation with polyethylene glycol 6000, ion exchange chromatography, and ultrafiltration. The enzyme is a trimer of 73000 Da units with a molecular mass of 216000 (determined by native-PAGE an d gel filtration); its pi is around 4.9. Enzyme activity measurments r ealized with 9-and 13-hydroperoxides of linoleic acid (9-La OOH and 13 -La OOH, respectively), alpha-linolenic acid (9-Ln OOH and 13-Ln OOH, respectively), and gamma-linolenic acid (9-gamma Ln OOH and 13-gamma-L n OOH, respectively) revealed a great affinity for 13-Ln OOH. The enzy me is rapidly inhibited by its substrate (13-Ln OOH), but preincubatio n with the other five hydroperoxides, which are not degraded by the en zyme, also resulted in activity inhibition. Dialysis could not restore the activity. When 13-Ln OOH is reduced in its corresponding alcohol or converted to its methyl ester, the inhibition is reduced.