Inhibition characteristics of peptide extracts of four medicinal plants on activities of bovine trypsin

Abstract

Aqueous extract of leaves of Momordica charantia, Hymenocardia acida, Lawsonia inermis and fruit of Xylopia aethiopica have been used in sub Saharan Africa in the management of many viral diseases. Their medicinal properties had been reported to be due to their high antioxidant activities, but limited information is available whether these properties are also due to inhibition or modulation of proteases important in the pathology of viral infections. We report the inhibitory characteristics of peptides extracted from these medicinal plants against bovine trypsin, a serine protease.Extraction of the peptides was done using standard procedure and their inhibitory activities were measured against bovine trypsin. Aqueous extract of M. charantia, H. acida, L. inermis and X. aethiopica contain 5.7 ± 0.5 mg/ml, 1.0 ± 0.2 mg/ml, 1.8 ± 0.1 mg/ml and 28.3 ± 4.1 mg/ml of peptides, respectively. Using Nα-benzoyl-DL-arginine 4-nitroanilide (BAPNA) as trypsin substrate, a Km and Vmax of 0.34 mM and 0.6 μmole/min/mg protein obtained, were altered in the presence of the peptide extracts suggesting the extracts modulate trypsin activity. The inhibition was either competitive, non-competitive or mixed-type of non-competitive inhibition. Inhibition constant (Ki) ranging from 81 to 831±120 μg/ml were obtained using Dixon plot with the peptide extract from M. charantia being the most potent.We concluded that the medicinal and antiviral properties of the extracts could also be due to inhibition or modulation of proteases involved in the pathology of viral infection.