Antioxidant peptides

Hou, W. C., Chen, H. J., and Lin, Y. H. (2003). Antioxidant peptides with angiotensin converting enzyme inhibitory activities and applications for angiotensin converting enzyme purification. ]. Agric. Food Chem. 51,1706-1709. 

As antioxidant peptides are rarely present in marine invertebrates, they must be released from the parent protein by hydrolysis with enzymes. Various enzymes have been used to release peptides from muscle proteins. To date, different muscle proteins have been extracted, hydrolysed, and their antioxidant activities studied, which is among all invertebrate muscles the most similar to vertebrate skeletal muscle. Various studies have been conducted to investigate the antioxidant properties of hydrolysates or bioactive peptides from marine invertebrate sources like oysters... 

In another study conducted on marine zooplankton (Byun et ah, 2009b), antioxidant activity was measured for the DPPH radical of hydrolysates produced by Alcalase, a-chymotrypsin, Neutrase, papain, pepsin, and trypsin. To identify antioxidant peptides, peptic hydrolysate was purified using consecutive chromatographic methods, and antioxidant peptides were identified to be Leu-Leu-Gly-Pro-Gly-Leu-Thr-Asn-His-Ala (MW 1076Da) and Asp-Leu-Gly-Leu-Gly-Leu-Pro-Gly-Ala-His (MW 1033Da) by Q-TOF ESI mass spectroscopy. IC50 values of purified peptides were... 

Philanto, A. (2006). Antioxidative peptides derived from milk proteins. Int. Dairy J. 16, 1306-1314. 

Qian, Z. J., Jung, W. K., and Kim, S. K. (2008a). Free radical scavenging activity of a novel antioxidative peptide purified from hydrolysate of bullfrog skin, Rana catesbeiana Shaw. Bioresour. Technol. 99,1690-1698. 

The antioxidant activity of peptides has been shown to be a result of the cooperative effect of their entire amino acid sequence however, there is still little information concerning the structural characteristics of antioxidative peptides. At present, the main strategy has been to identify and characterize antioxidative peptides from the hydrolysates of proteins ... 

The electronic property of the amino acid on the C-terminus also has an effect on antioxidant activity (Li et al., 2011), that is, the larger the electronic property, the higher is the activity. The C-terminus is a polar position that is thus affected by its electrostatic potential, to some extent therefore, the amino acids Trp, Glu, Leu, lie, Met, Val, Tyr, etc. are suitable at the C-terminus. Some researchers have speculated that the identity of the amino acid on the C-terminus would play an important role in its activity. Suetsuna (2000) separated and identified a radical scavenging peptide, Tyr-Phe-Tyr-Pro-Glu-Leu, from casein hydrolysate, and it was confirmed that the Glu-Leu on the C-terminus mainly contributed to its antioxidant activity. Kim et al. (2009) speculated that the hydrophobic property of the amino acid on the C-terminus, for example, Val and Leu, had a distinct effect on the activity, as determined from the analysis of antioxidative peptides derived from venison hydrolysate. 

Chen et al. (1996) investigated 28 synthetic peptides that were based on the antioxidative peptide Leu-Leu-Pro-His-His. They found that the deletion of the C-terminus His decreased the activity, whereas the deletion of the N-terminus Leu had no effect therefore, it seemed that the C-terminus was related to the antioxidative activity of the peptide, while the N-terminus had no effect. Saito et al. (2003) pointed out that two Tyr-containing tripeptides (Tyr-X-Tyr) showed higher activity than did two His-containing tripeptides (His-X-His). According to the structural characteristics, the hydrophobicity of an amino acid on the N-terminus is the most important property for activity with respect to the same amino acid in the central position in addition, Tyr on the N-terminus has stronger hydrophobicity than His. Therefore, it can be predicted that Tyr-X-Tyr has higher activity than His-X-His. 

Chen, H. M., Muramoto, K., and Yamauchi, F. (1995a). Structural analysis of antioxidative peptides from soybean p-conglydnin. J. Agric. Food Chem. 43, 574-578. 

Kim, S. Y., Je, J. Y., and Kim, S. K. (2007). Purification and characterization of antioxidant peptide from hoki (Johnius balengerii) frame protein by gastrointestinal digestion. J. Nutr. 

Klompong, V., Benjakul, S., Yachai, M., Visessanguan, W., Shahidi, F., and Hayes, K. D. (2009). Amino acid composition and antioxidative peptides from protein hydrolysates of yellow stripe trevally (Selaroides leptolepsis). J. Food Sci. 74,126-133. 

Sampath, K. N. S., Nazeer, R. A., and Jaiganesh, R. (2011). Purification and identification of antioxidant peptides from the skin protein hydrolysate of two marine fishes, horse mackerel (Magalaspis cordyla) and croaker (Otolithes ruber). Amino Acids, doi 10.1007/ s00726-011-0858-6. 

Suetsuna, K. (2000). Antioxidant peptides from the protease digest of prawn (Penaeus Japonicus) muscle. Mar. Biotechnol. 2, 5-10. 

Peptides derived from fish proteins have shown the ability of exerting potent antioxidative activities (Table 15.1) in different oxidative systems (Rajapakse et ah, 2005). Currently, an increasing interest exists to explore natural antioxidative substances without side effects and the identified antioxidative activities have potential to develop safe and nonhazardous natural antioxidants for the complications arose from oxidation of biomolecules. Je et ah (2007) purified an antioxidative peptide from tuna backbone protein and identified as VKAGFAWTANQQLS (1519Da) which was very important regarding the functional foods. It was reported that the derived peptides were good radical scavengers and antioxidant. 

In another study, an antioxidant peptide has been isolated from hoki frame protein by gastrointestinal digestion (Kim et ah, 2007). A number of enzymes have been used for the hydrolysis process, and the isolated peptides showed strong antioxidant activities in various model systems. 

TABLE 15.1 Potential bioactive antioxidative peptides derived from various fish proteins... 

ACE inhibitory peptides have been separated from the skin of skate by Lee et ah (2011). The purified peptides showed IC50 values of 95 and 148 M, respectively, for both peptides isolated from the skin of skate. Further, Lineweaver-Burk plots indicated that the peptides act as noncompetitive inhibitor against ACE. Recently, many inhibitory peptides against ACE are reported (Table 15.2) as natural alternative biofunctional peptides that are safer than that of the existing artificial ACE inhibitory compounds in the market that show some side effects. Various peptides have been isolated from seafood by-products from the fisheries industry such as backbones from tuna (Lee et al., 2010). Tuna backbone has hydrolyzed using various proteases such as alcalase, a-chymotrypsin, neutrase, papain, pepsin, and trypsin to obtain an antioxidant peptide (Je et ah, 2007). 

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