Purification and kinetic characterization of an anionic peroxidase from melon (Cucumis melo L.) cultivated under different salinity conditions

The partial characterization of an anionic peroxidase in melon fruit is des cribed. Four melon peroxidase (MPX) isoenzymes were detected in crude extra cts after isoelectric focusing. The major MPX isoenzyme (pI = 3.7) was part ially purified by including hydrophobic and anion-exchange chromatography i n the purification scheme. The sample obtained was used to characterize MPX . This peroxidase did not show activity on ascorbic acid but oxidized guaia col at a high rate, showing an optimum pH of 5.5 when acting on this last r educing substrate. Melon fruits grown under highly saline conditions showed slightly increased levels of this anionic isoenzyme. Kinetic studies using 2,2'-azinobis(3-ethylbenzothiazolinesulfonic acid) (ABTS) as reducing subs trate showed that increased salinity in the growth medium did not modify th e kinetic parameters of melon peroxidase on both hydrogen peroxide and redu cing substrate.