Screening of Angiotensin-I Converting Enzyme (ACE) Inhibitory Peptides from Thermolytic Hydrolysate of Arthrospira platensis

Angiotensin-I Converting Enzyme (ACE, EC 3.4.15.1) plays an essential role in controlling blood pressure. In this research, ACE inhibitors extracted from Arthrospira platensis thermolysin protease were provided using various chromatographic techniques, including reversed-phase high-performance liquid chromatography (RP-HPLC) and strong cation exchange chromatography (SCX). The amino acid sequence was determined by liquid-chromatography-tandem mass spectrometry (LC-MS/MS) and identified using two independent approaches: database-assisted identification and de novo sequencing. FY11 (FSESSAPEQHY) and IR5 (ILLYR) were established with the m/z 1281.54 and 677.37, respectively. The IC50 of IR5 from triplicate experiments was lower than FY11, with the value 10.54 +/- 1.38 mu M. IR5 was regarded as a non-competitive ACE inhibitor, with the docking interaction energy of - 106.842 kJ/mol. Docking results revealed that the interaction between ACE and peptide existed outside the ACE active site, excluding Arg 522, one of the Cl2 binding sites. Notably, the content of IR5 in 2 mg of crude thermolysin digest was determined to be 2.42 mu g/mg using LC-MS/MS quantification. Based on all these features, Arthrospira peptides can be considered to be a potentially promising antihypertensive agent.