Preparation, Characterization, and Antioxidant Properties of Phycocyanin Complexes Based on Sodium Alginate and Lysozyme.

In this study, phycocyanin-sodium alginate/lysozyme complex (PC-SLC) was prepared for the first time and characterized by UV spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and circular dichroism spectroscopy (CD). The stability of PC-SLC under light, temperature, pH and simulated gastrointestinal fluid was investigated. The scavenging ability of the complexes against DPPH and ABTS radicals was determined. The results showed that the complex formed by the mass ratio of SA-LZM of 0.1 showed the highest PC encapsulation rate (89.9 ± 0.374%). The combination of SA and LZM changed the secondary conformation of PC. The PC-SLC complex shows an irregular spherical structure and the spheres are clustered together. Compared with phycocyanin (PC), its thermal stability was obviously improved, but it was still greatly influenced by light. It could exist stably in simulated gastric fluid (SGF) for 2 h and be slowly digested in simulated intestinal fluid (SIF), which helped to promote the absorption of nutrients in the intestinal tract. Meanwhile, the complex PC-SLC showed high scavenging ability for DPPH and ABTS radicals. It can be concluded that the complexes have good antioxidant activity. This study provides an idea for the construction of PC delivery system and makes it more widely used in food industry and other fields.

ACE inhibitory activities of two peptides derived from Volutharpa ampullacea perryi hydrolysate and their protective effects on H2O2 induced HUVECs injury.

The purpose of this study is to explore the effects of IVTNWDDMEK and VGPAGPRG, two angiotensin I-converting enzyme (ACE) inhibitory peptides purified from Volutharpa ampullacea perryi, on ACE's two domains and on nitric oxide (NO), endothelin-1(ET-1) production in human vascular endothelial cells (HUVECs). In addition, we sought to investigate the effects of these two peptides on HUVECs injury induced by H2O2. The results indicated that the inhibition of the ACE C-domain was significantly higher than that of the ACE N-domain by these two peptides. Molecular dynamics (MD) analysis revealed that the hydrogen bonds interactions between ACE and two peptides, the chelation between peptides and Zn2+ both play important role, which might contribute significantly to the ACE inhibitory activity. Two peptides significantly increase NO and ET-1 production in a dose-dependent manner and protects against hydrogen peroxide-induced HUVEC cell injury. The reported results also show that two peptides up-regulated the expression of nuclear factor erythroid 2-related factor (Nrf2) and heme oxygenase-1 (HO-1), and reduce the accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA). Our study indicated that IVTNWDDMEK and VGPAGPRG could be potent ACE inhibitors and Volutharpa ampullacea perryi is a good source of bioactive peptides, which provided a theoretical basis for the broad application of two selected peptides as functional food with anti-hypertensive activity.

Study on the domain selective inhibition of angiotensin-converting enzyme (ACE) by food-derived tyrosine-containing dipeptides.

In this article, the selective inhibition of several tyrosine-containing dipeptides on N and C domain of ACE (angiotensin-converting enzyme) was studied, and the interaction mode of ACE and inhibitors was simulated by molecular docking. MTT assay was used to detect the effect of dipeptide on human umbilical vein endothelial cells (HUVEC). The results showed that the food-derived dipeptides AY (Ala-Tyr), LY (Leu-Tyr), and IY (Ile-Tyr) containing tyrosine at the C-terminal were favorable structures for selective inhibition of ACE C-domain. These dipeptides showed competitive and mixed inhibition patterns, while the dipeptides EY (Glu-Tyr), RY (Arg-Tyr), FY (Phe-Tyr), and SY (Ser-Tyr) showed noncompetitive inhibition. Food-derived dipeptides containing tyrosine have no cytotoxicity on HUVEC cells, which provides a basis for the application of food-derived tyrosine dipeptides as antihypertensive peptides. This study provides a theoretical basis for exploring the selective inhibition mechanism of ACE inhibitory peptides containing tyrosine residue. PRACTICAL APPLICATIONS: Angiotensin-converting enzyme (ACE) is a two-domain dipeptidyl carboxypeptidase, which is a key enzyme to regulate blood pressure. ACE has two active sites, C- and N-domain, which have high catalytic activity. Although the amino acid sequences of the two active sites have 60% similarity, there are some differences in structure and function. The action mechanism of ACE domain should be clarified, and the structure-activity relationship between inhibitors and ACE domain has not been systematically studied. The aim of this study was to identify the selective inhibitory effect of food-derived tyrosine dipeptides on the domain of ACE. This provides a new idea for finding new antihypertensive drugs with less side effects.