Studies on Dipeptidyl Peptidase-IV Inhibitory Activity of Protein Hydrolysates Derived from Tuna Cooking Juice

• Main Authors: Kit-Pan Ho, 何潔攀
• Other Authors: Kuo-Chiang Hsu
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/84662895045872619218

碩士 === 中國醫藥大學 === 營養學系碩士班 === 99 === Incretin hormones are defined as intestinal hormones released in response to nutrient ingestion, which exert a potent glucose-dependent insulinotropic action. It also suppresses glucagon secretion, slows gastric emptying and reduces appetite. Incretin is beneficial to provide glycemic control while avoiding hypoglycemia and weight gain. The half-life of incretin in the circulation is less than 2 minutes owing to the rapid inactivation by the ubiquitous proteolytic enzyme dipeptidyl peptidase-IV (DPP-IV). DPP-IV inhibitors have been investigated as a new therapy approach for the treatment of type 2 diabetes mellitus. The aim of this study was to utilize tuna cooking juice by-product as the material, to be hydrolyzed by Protease XXIII (PR) and Orientase (OR) for 0, 1, 2, 4, 6 h. The inhibitory effect of tuna cooking juice hydrolysates against DPP-IV activity was investigated, and the sequences of the DPP-IV inhibitory peptides were identified. The results were shown as follows: 1. The moisture, protein, lipid and ash contents of tuna cooking juice are 93.75, 5.44, 0.23 and 1.12%, respectively. In tuna cooking juice, glycine and histidine are the major constituted amino acids, and alanine and proline are the most abundant hydrophobic amino acids. 2. The degree of hydrolysis (DH) of tuna cooking juice with PR and OR at the enzyme concentration of 1 and 2 mg/mL increased dramatically during the first 60 min and then increased gradually thereafter. DHs of the hydrolysates obtained after 6 h hydrolysis by PR and OR were 23.5% and 19.4%, respectively. 3. The 1 h PR and OR hydrolysates had significantly (p<0.05) higher DPP-IV inhibitory activity than 0h hydrolysates, and their DPP-IV inhibitory activities were 36.2% and 36.9%, respectively. 4. After fractionation on a Sephadex G-25 gel filtration, PRH and ORH both had five (F1-5) major fractions. PRF2 and ORF2 showed the highest DPP-IV inhibitory activities of 39.5% and 38.8%, respectively among all the fractions, and their IC50 values were 7.0 mg/mL and 8.3 mg/mL. 5. Identification of the DPP-IV inhibitory peptides were accomplished with RP-HPLC, and five fractions (a-e) were obtained for both PRF2 and ORF2. The PRF2c and ORF2c showed the highest DPP-IV inhibitory activities of 19.5% and 14.8% at the concentration of 2 mg of dried extract/mL, respectively, as compared to the other fractions. 6. Finally, the amino acid sequences of the DPP-IV inhibitory peptides isolated from the PRF2c and ORF2c were identified: Pro-Ala-Cys-Gly-Gly-Phe-Try-Ile-Ser-Gly-Arg-Pro-Gly (1304.644 Da)、Cys-Ala-Tyr-Gln-Trp-Gln-Arg-Pro-Val-Asp-Arg-Ile-Arg (1690.879 Da)、Pro-Gly-Val-Gly-Gly-Pro-Leu-Gly-Pro-Ile-Gly-Pro-Cys-Tyr-Glu (1412.733 Da)。 The results showed that the peptides majorly constituted by hydrophobic amino acids and having the proline or alanine as the penultimate N-terminal residue possessed great DPP-IV inhibitory activity. Tuna cooking juice could be the potential source of DPP-IV inhibitor that may be used in the treatment of type 2 diabetes.