To investigate biomedical and nutraceutical benefits of bullfrog (Rana catesbeiana Shaw) muscle protein, we examined an angiotensin I-converting enzyme (ACE 1) inhibitory activity of various enzymatic hydrolystes of R. catesbeiana muscle protein in the present study. Among the enzymatic hydrolysates prepared using various commercial enzymes such as Alcalase, neutrase, pepsin, papain, (alpha-chymotrypsin, and trypsin, Alcalase-proteolytic hydrolysates showed the highest ACE I inhibitory activity. During consecutive purification using a Hiprep 16/10 DEAE FF anion exchange and an octadecylsilane (ODS) C 18 reversed phase liquid chromatographic techniques, a potent ACE I inhibitory peptide composed of 12 amino acids, Gly-Ala-Ala-Glu-Leu-Pro-Cys-Ser-Ala-Asp-Trp-Trp (M-w: 1.3 kDa) was isolated from R. catesbeiana muscle hydrolysates degraded by Alcalase. The purified peptide from R. catesbeiana muscle (RCMP-alca) has IC50 value of 0.95 mu M, and Lineweaver-Burk plots suggest that RCMP-alca play act as a non-competitive inhibitor against ACE I. Antiltypertensive effect in spontaneously hypertensive rats (SHR) also revealed that oral administration of RCMP-alca can decrease systolic blood pressure significantly (P < 0.05). In addition, MTT assay showed no cytotoxicity on human embryonic lung fibroblasts cell line (MRC-5). The result of this study suggests that the ACE inhibitory peptide derived from R. catesbeiana muscle (RCMP-alca) could be potential candidates to develop nutraceuticals and pharmaceuticals. (C) 2007 Elsevier Ltd. All rights reserved.