Design and Improvement of Food Proteins by the Introduction of New Function

在食品蛋白质的酶消化液中筛选生物活性多肽。合成了这些多肽的衍生物，并研究了它们的构效关系，从而设计出具有口服活性的多肽，通过蛋白质工程将其引入到食品蛋白质中。酪氨酸蛋白C(Casoxin C，Tyr-Ile-Pro-Ile-Gln-Tyr-Val-Leu-Ser-Arg)是牛酪蛋白在胰酶作用下产生的一种多功能多肽。在酪毒素C的羧基末端的五肽序列与层粘连蛋白五肽Tyr-Ile-Gly-Ser-Arg之间存在同源性。与层粘连蛋白五肽不同，酪毒素C或其羧基末端的多肽不能抑制肿瘤转移。[Ile^7，Gly^8]-Casoxin C的羧基末端含有层粘连蛋白五肽序列，可抑制小鼠的肿瘤转移。Casoxin D，Tyr-Val-Pro-Phe-Pro-Phe是一种来源于人α-酪蛋白的血管松弛多肽。Casoxin D与内皮细胞上的缓激肽BK1受体结合。由酪毒素D刺激释放的内皮衍生的松弛因子是前列环素。在合成的酪毒素D衍生物中，Tyr-Pro-Phe-Pro-Phe、Val-Val-Phe-Pro-Pro-Phe和Tyr-Val-Phe-Pro-Pro-Phe在1/4、1/7和1/10的浓度下对自发性高血压大鼠表现出血管松弛活性，而其他多肽仅在静脉给药后具有降血压作用。另一种衍生物Tyr-Pro-Phe-Pro-Pro-Leu在浓度为酪蛋白D的1/10000时表现出松弛血管的活性，其作用方式与酪蛋白D不同。从小麦面筋蛋白的酶解液中分离得到多肽，通过取代单一氨基酸残基得到有效的衍生物。

Biologically active peptides are screened for in enzymatic digests of food proteins. Derivatives of theses peptides were synthesized and their structure-activity relationships were studied to design orally effective biologically active peptides, which could be introduced into food proteins by protein engineering. Casoxin C, Tyr- Ile-Pro-Ile-Gln-Tyr-Val-Leu-Ser-Arg, which is released from bovine kappa-casein by the action of trypsin is a multifunctional peptide. Homology is found between the penta- peptide sequence at the carboxyl terminus of casoxin C and the laminin penta-peptide, Tyr-Ile-Gly-Ser-Arg. Unlike laminin penta-peptide, casoxin C or pepta-peptide at its carboxyl terminus did not inhibit tumor metastasis. The [Ile^7,Gly^8]-casoxin C, which has laminin penta-peptide sequence at the carboxyl terminus inhibited tumor metastasis in mice.Casoxin D, Tyr-Val-Pro-Phe-Pro-Pro-Phe, is a vaso-relaxing peptide derived from human alpha_<51>-casein. Casoxin D binds to bradykinin BK1-receptors of endothelium. The endothelium-derived relaxing factor released by casoxin D stimulusis is prostacyclin. Among casoxin D derivatives synthesized, Tyr-Pro-Phe-Pro-Pro-Phe, Val-Val-Phe-Pro- Pro-Phe and Tyr-Val-Phe-Pro-Pro-Phe showed vaso-relaxing activity at the concentrations 1/4, 1/7 and 1/10 that of casoxin D. Tyr-Pro-Phe-Pro-Pro-Phe lowered blood pressure of spontaneously hypertensive rats after oral administration while other peptides were active only after intravenous administration. Another derivative Tyr- Pro-Phe-Pro-Pro-Leu showed vaso-relaxing activity at the concentration 1/10,000 that of casoxin D. Mode of action of this peptide was different from that of casoxin D.Opioid peptides were isolated from enzymatic digests of wheat gluten and potent derivatives were obtained by substitution of single amino acid residues.