Chemical Properties of Bioactive Peptides Originated from Common Food Products

Chemical Properties of Bioactive Peptides Originated from Common Food Products Abstract In recent years, a number of endogenous and food-derived proteins have been identified as potential sources of opioid or opiomimetic peptides. They include gluten, meat and caseins. By limited proteolysis of such proteins, a number of peptides have been identified, which presents features of opiomimetic action: binding to opioid receptors, competition for opioid ligands, opiomimetic effect, and reversion of their action by the addition of opioid antagonists. The advances in the research field of bioactive peptides are driven by a molecular understanding of biological processes and analytical tecniques are a critical component of this understanding. Different up-to-date methods, including peptide synthesis and immunochemistry, have been applied to the chemical characterization of bioactive peptides. The question of what kinds of bioactive peptides are beneficial and desirable as food constituents or as 'drugs' should be always carefully examined. However, the possibilities for the design of dietary products and 'natural' drugs look promising. Peptidic fragments with opioid activity have been found in human, bovine, ovine, and water buffalo ?-caseine, which are named ?-casomorphines [1,2]. The opioid peptides are known to regulate many immune functions, including stress and pain. In the present communication we report the synthesis and structure-activity studies of a series of peptides that are analogues of functional peptides found in milk proteins. Specifically we report about a series of peptides that, when provided by casein, show opioid activity. Conformational studies in solution and in the crystalline state in conjunction with theoretical conformational analysis are important, since they provide information about the conformational behaviour of the peptide and about the energy content of various possible conformers. This kind of information can be expected to contribute toward a better understanding of conformational and thermodynamic aspects of the interaction with opioid receptors. Finally, the possible application of the bioactive peptides for functional foods, based on the study of opioid peptides, will be discussed. Furthermore we have synthesized a series of peptides derived from gluten proteins (gluten exorphins) [3] in order to investigate the possible effect of this opioid in pituitary hormon secretion, particularly in patients with coeliac disease. [1] Maubois J.L. and Léonil J. (1989) Lait 69, 245-269 [2] Meisel H., (1997) Biopolymers (sec. Peptide Science) 43; 119-128 [3] Fukudome S. and Yoshikawa M. (1992) FEBS Lett. 296, 107-111