Seven kinds of angiotensin I-converting enzyme (ACE) inhibitory peptides were isolated from the hydrolysates of wakame (Undaria pinnatifida) by Protease S "Amano" (from Bacillus stearothermophilus) by using three-step high-performance liquid chromatography (HPLC) on a reverse-phase column. These peptides were identified by amino acid composition analysis, sequence analysis, and liquid chromatography-mass spectrometry (LC-MS), as Val-Tyr (IC(50) = 35.2 microM), Ile-Tyr (6.1 microM), Ala-Trp (18.8 microM), Phe-Tyr (42.3 microM), Val-Trp (3.3 microM), Ile-Trp (1.5 microM), and Leu-Trp (23.6 microM). These peptides have resistance against gastrointestinal proteases in vitro. Each peptide was determined to have an antihypertensive effect after a single oral administration in spontaneously hypertensive rats (SHR). Among them, the blood pressure significantly decreased by Val-Tyr, Ile-Tyr, Phe-Tyr, and Ile-Trp in a dose of 1 mg/kg of body weight (BW). The present study showed that antihypertensive effect in the hydrolysates of wakame by Protease S "Amano" was attributed to these peptides.

Brown alga ( Undaria pinnatifida ) was treated with alginate lyase and hydrolyzed using 17 kinds of proteases and the inhibitory activity of the hydrolysates for the angiotensin-I-converting enzyme (ACE) was measured. Four hydrolysates with potent ACE-inhibitory activity were administered singly and orally to spontaneously hypertensive rats (SHRs). The systolic blood pressure of SHRs decreases significantly after single oral administration of the brown alga hydrolysates by protease S 'Amano' (from Bacillus stearothermophilus) at the concentration of 10 (mg protein) (kg body weight) -1. In the 17 weeks of feeding experiment, 7-week-old SHRs were fed standard diet supplemented with the brown alga hydrolysates for 10 weeks. In SHRs fed 1.0 and 0.1% brown alga hydrolysates, elevating of systolic bloodpressure was significantly suppressed for 7 weeks. To elucidate the active components, the brown alga hydrolysates were fractionated by 1-butanol extraction and HPLC on a reverse-phase column. Seven kinds of ACE-inhibitory peptides were isolated and identified by amino acid composition analysis, sequence analysis, and LC-MS with the results Val-Tyr, Ile-Tyr, Ala-Trp, Phe-Tyr, Val-Trp, Ile-Trp, and Leu-Trp. Each peptide was determined to have an antihypertensive effect after a single oral administration in SHRs. The brown alga hydrolysates were also confirmed to decrease the blood pressure in humans.