Assays for angiotensin converting enzyme inhibitory activity

A colorimetric method and a capillary electrophoresis procedure were develo ped for quantifying histidyl-leucine and hippurate, respectively. The color imetric method is sensitive (extinction coefficient = 7.5 mM(-1) cm(-1)) an d reproducible (CV = 1.7%, n = 5), which is based on a selective chromogeni c reaction for histidyl-leucine (lambda (max) = 390 nm) using omicron -phth alaldehyde. For samples containing unusually high levels of histidine and/o r histidyl peptides, the separation-based approach is preferable. The capil lary electrophoresis method makes use of an in-capillary microextraction te chnique; complicated samples can be measured in less than 4 min without pre treatment, Protocols using both methods to measure angiotensin converting e nzyme inhibitory activity were proposed. (C) 2001 Academic Press.