The aim of this study was to find an experimental procedure to purify biologically active peptides from a complex biological matrix (plasma), which was incubated with a protease-rich extract (submandibular gland extract). Special interest was focused on the practicability of cross-flow filtration for this purpose. Therefore, peptides in the incubation mixture were purified with a combination of high-performance liquid chromatographic steps. Purification of biologically active peptides was monitored by a sensitive bioassay and by laser desorption/ionization mass spectrometry. This permitted not only purity control at each purification step but also identification of one of the peptides with vasoconstrictor properties as angiotensin II. This result demonstrates the practicability of cross-flow filtration for extracting enzymatic reaction products from complex substrate-enzyme mixtures during the incubation.
