Biochemical Study of Dipeptidylpeptidase-4 from Normal Human Serum

The research includes partial purification of dipeptidylpeptidase-4 (DPP-4) from serum of normal person aging 14 years in Mosul city. Gel filtration of dialysate precipitate produced by 50% ammonium sulphate saturation has given two major proteinous components. One of them (peak A) possesses a high DPP-4 activity using sephedex G-100. The apparent molecular weight of the isolated DPP-4 was 176.6 KD. High performance liquid chromatography HPLC revealed a single peak A at retention time 5.829 min by application the top of peak A which was isolated from gel filtration. Maximum activity of DPP-4 was obtained using 0.1 M Tris-HCl buffer at pH 8, 40C, 4 mM of gly-pro-p-nitroanilide hydrochloride as a substrate. The concentration 0.35 mg/ml partially purified DPP-4 was used for next experiments. Maximum velocity (Vmax) was 50 M according to Line Weaver-Burk plot while MichaelisMenten constant (Km) was 0.5 mM. Mercuric chloride and strontium chloride hexahydrate at 5 mM revealed maximum inhibitory effect of DPP4 activity by 30.2% and 42.9% respectively.