Yeast protease B-digested skimmed milk inhibits angiotensin-I-converting-enzyme activity

Angiotensin-1-converting-enzyme (ACE) inhibitory activity was identified in skimmed milk digested with cell-free extract of yeast Saccharomyces cerevisiae. Simultaneously, a protease enzyme involved in the production of ACE-inhibition materials in digested skimmed milk was purified to homogeneity from the cell-free extracts of S. cerevisiae by ammonium sulphate fractionation and chromatography in DEAE-Sephacel, D-tryptophan methyl ester-Sepharose 4B, Hiload Superdex G-200 and HPLC Mono-Q chromatography. The purified enzyme was identified as protease B, based on the molecular mass on SDS/PAGE and the N-terminal amino acid sequence of the enzyme. The optimum pH for digestion of skimmed milk and production of ACE-inhibition materials was pH 4.8. The IC(50) of the hydrolysate was 0.42 mg of protein/ml when skimmed milk was digested with yeast protease B.