Antihypertensive effects of silk fibroin hydrolysate by alcalase and purification of an ACE inhibitory dipeptide.

Silk fibroin, which is normally discarded as an industrial byproduct in clothing plants, was hydrolyzed with alcalase. Angiotensin I converting enzyme (ACE) inhibitory activities of the silk fibroin hydrolysates (SFH) were investigated, and the hydrolysate with hydrolysis degree of 17% exhibited the highest ACE inhibitory activity. At the tested 600 mg/kg.d and 1200 mg/kg x d doses, SFH significantly lowered blood pressure of spontaneously hypertensive rats (SHR) after chronic oral administration. SFH was further purified using consecutive chromatographic methods on Sephadex G-15 column and reverse phase high-performance liquid chromatography (RP-HPLC) on an octadecylsilane column. After its purity was confirmed by analytical RP-HPLC and capillary electrophoresis, one ACE inhibitory dipeptide was isolated, and its molecular mass and amino acid sequence were determined as 238.2 Da and Gly-Tyr, respectively, by LC-ESI/MS. The results of this study suggest that silk fibroin byproducts have the possibility to become an effective source for ACE inhibitory peptides.