Abstract
Five novel peptides (LPLF, WLQL, LPSW, VPGLAL, and LVGLPL) bearing dipeptidyl peptidase IV (DPP-IV) inhibitory activities were identified from the gastrointestinal enzymatic hydrolysate of soft-shelled turtle yolk (SSTY) proteins. Peptides were isolated separately using reversed-phase (RP) chromatography in parallel with off-line strong cation exchange (SCX) chromatography followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis to determine sequences. Among these peptides, LPSW showed the highest DPP-IV inhibitory activity with an IC50 value of 269.7 ± 15.91 µM. The results of the pre-incubation experiment and the kinetic study of these peptides indicated that WLQL is a true inhibitor and its inhibition toward DPP-IV is of an uncompetitive model, while LPLF, LPSW, and VPGLAL are real-substrates and competitive inhibitors against DPP-IV. The DPP-IV inhibitory peptides derived from SSTY hydrolysate in study are promising in the management of hyperglycemia in Type 2 diabetes.
Highlights
The egg of soft-shelled turtle (SST) (Pelodiscus sinensis), a valuable aquaculture product in Taiwan and other Asian countries, is widely consumed as a tonic food in traditional Chinese medicine [1]
This study aimed to screen the dipeptidyl peptidase IV (DPP-IV) inhibitory peptides from soft-shelled turtle yolk (SSTY) hydrolysates selected from several enzymatic digests using two independent bioassay-guided fractionations; strong cation-exchange (SCX) chromatography and reversed-phase high-performance liquid chromatography (RP-HPLC)
Lipids were eliminated from the SSTY protein to optimize enzymatic digestion activities and for further LC-MS/MS analysis
Summary
The egg of soft-shelled turtle (SST) (Pelodiscus sinensis), a valuable aquaculture product in Taiwan and other Asian countries, is widely consumed as a tonic food in traditional Chinese medicine [1]. The soft-shelled turtle egg has been utilized for its biofunctional benefits, such as cholesterol-lowering effects and antihypertensive activities [2,3,4,5,6]. Hydrolyzed soft-shelled turtle yolk (SSTY) proteins may be utilized in the control of type 2 diabetes via their capacity to inhibit DPP-IV. Bioactive peptides contain few amino acids that are inactive in the parent protein [8] These peptides exhibit a positive health impact on the human body after proteolytic digestion [9,10]. For this reason, they should be degraded from parent protein using enzymatic hydrolysis, microbial fermentation, gastrointestinal digestion, or other physical conditions [11,12]
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