Angiotensin I-converting enzyme inhibitory activity of purified proteins and peptides from the rhizomes of zingiberaceae plants

Abstract

Angiotensin I- converting enzyme (ACE) plays a major role in the regulation of blood pressure by virtue of two different reactions that it catalyzes: conversion of the inactive decapeptide angiotensin I to a powerful vasoconstrictor and salt-retaining octapeptide angiotensin II, and inactivation of the vasodilator and natriuretic nonapeptide, bradykinin. Blood pressure-lowering activities of pure protein and pepsin hydrolysates of protein of Zingiberaceae plants were assayed in vitro by inhibition of the angiotensin I-converting enzyme. The crude protein of 15 plants in Zingiberaceae family were screened for their ACE inhibitory by in vitro ACE inhibitory activity protein was isolated from Zingiberaceae plants. Crude protein of Z. ottensi. rhizome was high activity, having IC50 of 7.30×10-7 mg protein/ml. Rhizomes proteins were isolated and then purified by stepwise eluted SP sepharose chromatography. Five unbound fractions obtained from purification step were called F25, F50, F75, and F100. The highest protein content was found in the F75 fraction. Results form native and reducing SDS-PAGE indicated that the F75 was single protein gave an estimated size of about 20.7 kDa. The tryptic fragments of the ACEI were sequenced using LC-MS/MS analysis, it resulted suggested that its amino acid sequence is similar to chitinase. The effect ACEI activity of F75 was largely stable at temperature between -20 and 60 °C (at a 30 min exposure). The pH inhibition effect of fraction F75 was negated at pH 6 and steeply reduced at pH 8 – 12. This protein exhibited a strong ACE inhibitory activity which Ki was of 9.1 × 10-5 mg protein/ml. For the analysis of peptides from Z. cassumunar which derived from pepsin hydrolysates at 37oC for 30 min possessed ACE inhibition at IC50 of 0.38±0.012 mg/ml, after fractionation by RP-HPLC was ascribed to a single peptide with IC50 for ACE inhibitory at 0.011±0.012 mg/ml. The peptide was a potent competitive inhibitor of ACE with a Ki of 1.25 × 10-6 mg protein/ml. The sequence of the peptide from Z. cassumunar was found to be Pro-Ala-Glu-Gly-His-Ser, which is similar to the mitochondrial protein sequence from Solanum tuberosum L.