Activity Staining and Inhibition Characterization of Dipeptidylpeptidase-III Enzyme from Goat Brain

Dipeptidylpeptidase-III (DPP-III) from goat brain was purified and characterized using Arginyl-Arginyl-4-methoxy-β-naphthylamide (Arg-Arg-4mβNA) substrate. This enzyme retained its activity in native 10% polyacrylamide gel when stained using Arg-Arg-4mβNA. The activity was significantly increased by 100 mM chloride. Studies for its inhibition with some peptides and chemical inhibitors revealed that Leu-Trp-Met-Arg-Phe-Ala was most potent inhibitor followed by Arg-Phe-Ala and Gly-Phe-Leu. All the studied chemical inhibitors caused 40-50% inhibition at 1 mM. Metal ions helped to regain activity of EDTA pretreated enzyme. ZnCl(2) at 50 μM almost completely restored the enzyme activity. Further ZnCl(2) and CoCl(2) exerted protective effects on EDTA pretreated enzyme for its susceptibility to DTNB inhibition. Therefore, DPP-III is a metalloprotease with the involvement of cysteine residues either located at the catalytic site or involved in regulation.