Isolation from alpha-zein of thermolysin peptides with angiotensin I-converting enzyme inhibitory activity.

Urea-denatured alpha-zein was almost completely hydrolyzed into small peptides by digestion with 1/100 (w/w) of thermolysin at 37 degrees C for 3h. The angiotensin I-converting enzyme (ACE) inhibitory activity (IC50) of the thermolysin digest of total alpha-zein was 24.5 micrograms/ml, and most of the peptide fractions from Z19 alpha-zein and total alpha-zein separated by reverse-phase HPLC had more or less ACE inhibitory activity. From these fractions, thirty-six peptides, including 5 dipeptides, 14 tripeptides, 9 tetrapeptides, 5 pentapeptides, and 3 hexapeptides, were purified and their amino acid sequences were determined.