Inhibition of angiotensin I-converting enzyme by wheat gliadin hydrolysates

A tryptic gliadin hydrolysate was fractionated into peptide fractions, which were assigned to either the central domain (CD) or terminal domains (TD) of gliadins. The domains were expected to contain amino acid (AA) sequences which, when released from the parent protein, inhibit the angiotensin I-converting enzyme (ACE), which plays a key role in regulating blood pressure. A proline (Pro) poor TD related fraction, containing the smallest peptides, showed the highest ACE inhibitory activity (IC50 = 0.33 mg/ml). Additional peptidases were selected based on their in silico predicted ability to release ACE inhibitory peptides. Further hydrolysis of the tryptic hydrolysate fractions with thermolysin, Clarex, Alcalase and Esperase increased ACE inhibitory activities. Immobilised Ni2+-ion affinity chromatography (IMAC) purification of a TD related peptide fraction obtained by sequential hydrolysis with trypsin and thermolysin yielded a fraction with an IC50 value of 0.02 mg/ml. This IMAC fraction was enriched in histidine and hydrophobic AA (Pro, Val, Ile, Leu and Phe).

Research highlights
► Thermolysin yields high ACE inhibitory peptides from gliadin.
► Purification by IMAC resulted in a peptide fraction with a clearly decreased IC50 value.
► It is not clear whether the TD or CD is a better precursor for ACE inhibitory peptides.