Introduction: Angiotensin converting enzyme (ACE) plays a major role in the regulation of blood pressure. ACE inhibitory peptides can effective on treatment of hypertensive. The aim of this research is to determine the inhibitory pattern of purified peptides from tryptic HEWL on ACE activity and also obtaining kinetic parameters. Methods: The HEWL protein (0.25 gram) was hydrolyzed by treatment with trypsin for 2hrs in 37 ºC. The enzymatic hydrolysis stopped by boiling for 15 min. The resulted solution centrifuged at 10000 RPM for 10 min and the supernatant solution was ulterafiltered and utterance of 10 kDa peptides were lyophilized and sub-fractionated using HPLC. A linear gradient of 5-25% acetonitrile in 0.1% TFA at flow rate of 2 ml/min was applied over 30 min and monitored the absorbance of 220 nm using UV detector. Finally ACE inhibitory effects of major peaks were studied. Inhibition mode of purified peptides and kinetic parameters of Km and Vmax were determined by line weave-Burk plot. Results: Our research showed that in presence tryptic hydrolysate the absorbance of 340 nm reduced less than from the control that showed those have ACE inhibitory activity. Among these purified peptides, F3 fraction has the most of %ACE inhibitory and least of IC50. The 50% inhibitory concentration (IC50) of this peptide was 64µg/µl. kinetic parameters of Vmax and Km in absence of inhibitory peptide were 0.061, 0.415 and in presence inhibitory peptide were 0.017, 0.145 in respectively. Conclusion: The kinetic results showed that the mechanism of inhibitory activity was non-competitive which means that F3 fraction cannot bind active site of ACE. Finally HEWL tryptic hydrolysates may serve as useful source in the formulation of antihypertensive drugs and functional foods.

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