DIPEPTIDYL PEPTIDASE-IV IN GHERKIN SEEDLINGS CUCUMIS-SATIVUS L CV PALAVA

The properties and organ localization of dipeptidyl peptidase IV (DPP IV; EC 3.4.14.5) were described in relation to a study of the utilizat ion mechanism of stored proteins and peptides during 7 days of germina tion of gherkin seeds (Cucumis sativus L. cv. Palava). During germinat ion the enzyme activity in the embryonic axis showed a decrease, while no substantial changes were found in its activity in the cotyledons. At the stage when the roots and hypocotyls could be morphologically di stinguished, the activity of DPP IV increased in both organs, approach ing the maximum on day 6 of germination. After electrophoretic separat ion of extracts from the embryonic axis, roots, hypocotyls and cotyled ons, respectively, only a single band of DPP IV was observed (R(f) = 0 .37). The pH optimum of DPP IV was 8, apparent K-m Gly-Pro-beta NA = 3 .10(-4) mol.l(-1); diisopropyl fluorophosphate (DFP) at the concentrat ion of 10(-3) mol.l(-1) completely inhibited its activity. Histochemic ally, the highest activity of the enzyme investigated in sections of r oots and hypocotyls was found in the vascular bundles, in the epidermi s and in the subepidermal layer of the bark. The results confirmed the participation of DPP IV in the mobilization and/or utilization of sto red proteins and peptides during germination of gherkin seeds.