Characterization of soluble and bound peroxidases from artichoke heads and leaves.

In plants, peroxidase (POD) is present in both soluble and bound forms; the first one is distributed within both the intra- and extracellular environment while the bound ones are considered to be associated with plant cell walls. In this paper the characterization of soluble (SP), ionically bound (IBP) and covalently bound (CBP) peroxidases from artichoke (Cynara cardunculus L. subsp. scolymus (L.) Hayek) leaves and heads were performed. The three forms were analyzed by SDS-PAGE and IEF (pH range 3.5-9.5) and stained for POD activity. SP and IBP had a similar pattern with two groups of bands very evident at 60 KDa and 35 KDa and another zone at 100 KDa with light intensity, while CBP showed two groups of bands with molecular weight within 60 and 90 KDa. All the PODs showed a basic isoform (pI 9.5). Furthermore IBP from heads presents another basic isoform with pI slightly lower than 9.5, but no acidic components were detected. SP and CBP, instead demonstrated the presence of several acidic isoforms, one band with pI 3.5 and another groups of bands with pI ranging between 4.5 and 6. The SP, IBP and CBP oxidized guaiacol very quickly but showed no detectable activity toward ascorbic acid and veratryl alcohol. It demonstrated that these enzymes are related to the Class III peroxidases. When guiacol was used as substrate the optimum pH of the POD forms ranged between 5.5 and 6.5. The POD forms showed a high stability after 10 min at temperatures between 5°C and 65°C but after 10 min at 85°C, the enzymes were almost inactivated. When the enzymatic activity was reduced to 40% of the original, and after an incubation period of 1hr at 30°C, the bounded PODs are more able to regenerate themselves than the soluble one.