title: Rapid and simple colorimetric assay for screening angiotensin I-converting enzyme inhibitors.
abstract: BACKGROUND
  Angiotensin-converting enzyme (ACE) is one of the main regulators of blood pressure through its action on the renin-angiotensin system. ACE inhibitory peptides from natural materials inhibit ACE activity and have considerable importance as antihypertensive agents.
  
  
  OBJECTIVE
  A new chromogenic reaction method for determining hippuric acid (HA) and angiotensin I-converting enzyme (ACE) inhibitor activity was developed.
  
  
  METHODS
  This method is based on the reaction of HA with p-dimethylaminobenzaldehyde in the presence of quinoline, acetate, and acetic anhydride. The red-orange formation product in the reaction has a stable absorbance in the visible region and it was determined at 478 nm. The assay conditions were optimized and by using an ACE concentration of 12 mU/mL in enzymatic reaction, the method was applied to monitor the IC(50) values (the concentration of inhibitor required to inhibit 50% of the ACE activity) for captopril and Saurida elongata (Synodontidae) muscle protein hydrolyzate.
  
  
  RESULTS
  With the proposed method, IC(50) values for captopril and Saurida elongata muscle protein hydrolyzate were determined as 0.0123 µM and 0.1648 mg/mL, respectively. Those results correspond to the IC(50) values of 0.0109 µM and 0.1820 mg/mL obtained by high-performance liquid chromatography (HPLC) method.
  
  
  CONCLUSIONS
  The proposed method is rapid, accurate, reproducible and convenient, and suitable for screening ACE inhibitor peptides from food materials while it does not require HA extraction from the components of the ACE activity assay reaction.
authors.affiliation: School of Chemistry and Chemical Engineering, Guangxi University, Nanning, Guangxi, PR China.
authors.forename: Shanguang
authors.initials: S
authors.lastname: Wu
authors.forename: Jianhua
authors.initials: J
authors.lastname: Sun
authors.forename: Zhangfa
authors.initials: Z
authors.lastname: Tong
authors.forename: Xiongdiao
authors.initials: X
authors.lastname: Lan
authors.forename: Bing
authors.initials: B
authors.lastname: Shu
authors.forename: Youyan
authors.initials: Y
authors.lastname: Liu
authors.forename: Dankui
authors.initials: D
authors.lastname: Liao
mesh_terms: D000806:Angiotensin-Converting Enzyme Inhibitors / Q000008:administration & dosage / Q000737:chemistry / Q000494:pharmacology*; D000818:Animals; D002216:Captopril / Q000008:administration & dosage / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D003124:Colorimetry / Q000379:methods*; D005399:Fishes; D006626:Hippurates / Q000737:chemistry; D020128:Inhibitory Concentration 50; D011492:Protein Hydrolysates / Q000008:administration & dosage / Q000494:pharmacology; D015203:Reproducibility of Results
chemical_list: D000806:Angiotensin-Converting Enzyme Inhibitors; D006626:Hippurates; D011492:Protein Hydrolysates; D002216:Captopril; C030514:hippuric acid