A convenient and accurate reversed-phase high-performance liquid chromatography (RP-HPLC) method for angiotensin I-converting enzyme inhibitory peptides assay was described in this paper. The mobile phase consisted of 70% A (0.05% TFA and 0.05% triethylamine in water, pH = 2.9–3.3) and 30% B (100% acetonitrile) using an Isogradient program. The flow rate was 0.5？mL/min. The absorb wavelength was 226.5？nm; the column temperature was controlled at 25°C. This method for angiotensin I-converting enzyme inhibitory peptides assay was convenient for the Iso-gradient program. The accuracy of the RT-HPLC method was verified by analyzing ACE inhibitory activity of the hydrolysate peptides of silkworm pupae protein, and the results showed that the RT-HPLC method was available for exploring new source of angiotensin I-converting enzyme inhibitory peptides rapidly and veraciously. 1. Introduction Angiotensin-converting enzyme (ACE) is a di-peptidyl carboxypeptidase (EC 3.4.15.1) associated with the blood pressure regulation system of renin-angiotensin. This enzyme can increase blood pressure by converting decapeptide angiotensin I into potent vasoconstricting octapeptide angiotensin II, which leads to a consistent increasing of blood pressure. ACE has been recognized as critical in the renin-angiotensin-aldosterone system (RAAS) for leading to hypertension [1]. Over the last reports, the first ACE peptide inhibitor was discovered from snake venom due to its significant effects on the hypertension. Afterwards, more and more potent synthetic inhibitors of ACE, such as captopril and enalapril, were found continuously. Currently, the application of ACE peptide inhibitors has become an important way to cure hypertension, congestive heart failure (CHF), and chronic renal disease [2], but its side effects to the health are also noticeable [3]. Therefore, the bioactive peptides with ACE inhibitory activity were paid more and more attentiones because of their curative and nontoxic characteristics, especially the food-derived ACE inhibitory peptides, isolated from food or enzymatic digestion of food proteins, such as from gelatin [4], casein [5], fish [6], fig tree latex [7], α-zein [8], cereals and legumes [9], fermented soybean food products [10], soy protein [11], edible mushrooms [12], and microbes [13] that have been successfully used. These anti-ACE peptides derived from food protein hydrolysates might be used as main ingredients of blood pressure-lowering functional foods and nutriments [14]. In order to facilitate the identification and isolation of peptides with
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