engleski

HUMAN AND RAT DIPEPTIDYL PEPTIDASE III: METALLOENZYMES WITH HIGHLY REACTIVE, FUNCTIONALLY IMPORTANT CYSTEINE RESIDUES

Dipeptidyl peptidase III (DPP III) is a cytosolic zinc-exopeptidase involved in the final steps of intracellular protein catabolism of eukaryotes. The regulatory role of DPP III in the metabolism of biologically active peptides (angiotensins and enkephalins) has been suggested. Our previous results indicated that enhanced expression of DPP III might be used as clinical marker for endometrial and ovarian cancer. The cDNA encoding the rat and human DPP III has been recently cloned and sequenced, revealing 93% identity of their primary structure. However, 3-D structure, physiological significance and regulation of DPP III still need to be elucidated. We have purified DPP III from human and rat erythrocytes using an identical procedure and determined its physico-chemical properties. The parallel biochemical investigation of the two enzymes revealed pronounced similarities but also significant differences indicating non-identity in their active site topology. The inactivation kinetics by sulphydryl reagent para-hydroxy-mercuribenzoate (pHMB) was monitored and the second order rate constants were calculated, revealing rat DPP III to be hyperreactive. Peptide substrates protected both enzymes from inactivation by pHMB indicating that reactive cysteine residues are part of the substrate-binding site. Because the biological thiols, oxidised glutathione and H2O2 influenced the activity "in vitro", we postulated that reversible redox regulation of zinc-enzyme DPP III could be of physiological importance. The study of modulation of this peptidase level under cellular stress conditions using proteomic approach is ongoing.

Dipeptidyl peptidase III; metalloenzymes; reactive SH-groups; redox regulation

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