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[Purification and identification of a novel ACE inhibitory peptide derived from the mud snail Bellamya purificata by RP-HPLC/MALDI-TOF MS].

Bellamya purificata is one of mud snails in fresh water found in China. The purification and identification of an angiotensin I-converting enzyme (ACE) inhibitory peptide extracted from Bellamya purificata hydrolysate are described. The peptide was purified twice with semi-preparative reversed-phase high performance liquid chromatography (RP-HPLC) to obtain an active fraction with an inhibitory concentration 50% (IC50) of 43.5 micromol/L. The primary structure of the purified peptide was identified by the high performance liquid chromatography/electrospray ionization mass spectrometry (HPLC/ESI-MS) and the martix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) combining with the amino acid composition analysis. Finally, it was identified as a tetrapeptide and sequenced as Lys-Glu-Ile-Trp (KEIW), which has the common characters of ACE inhibitory peptide extracted from selfish muscle. The structure identification results from the two methods were also compared in this study. The results from ESI-MS included a lot of information, such as the total ion current chromatogram and ultraviolet scan spectrum. However, the exact structure could only be from the MALDI-TOF MS analysis, in which the exact MS/MS spectrum could be obtained. Furthermore, the m/z measurement precision of MALDI-TOF MS was 0.0001 and much better than that of 0.1 of ESI-MS.