Biochemical Study of Dipeptidyl Peptidase-4 in Autistic's Patients

Abstract

The research includes estimation of autistics' serum dipeptidyl peptidase-4 (DPP-4) activity. The results indicated a significant (p≤0.05) decrease in (DPP-4) activity of autism spectrum disorder groups, 57.85, 42.86, 36.47 µmol/L respectively compared to control group. By statistical analysis, the study revealed a significant (p≤0.05) relationship between DPP-4 activity with gastrointestinal disorder on one hand and with various inflammation incidence on the other hand. Partial purification of DPP-4 from serum of normal person age 14 years in Mosul city was done. 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. Then SDS-PAGE was performed. 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, 40°C, 4 mM of gly-pro-p-nitroanilide hydrochloride as a substrate. Maximum velocity (Vmax) was 50 μM according to Line Weaver-Burk plot while Michaelis–Menten 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.