食品和醫(yī)療保健應用：抗菌肽

抗菌肽在生活中無處不在，它們常常是低分子量(2-5 kDa)，有時又被稱作防御素，長度通常在12至50個氨基酸之間。根據(jù)它們的結(jié)構特性，可歸為以下4類。

1. 螺旋肽:

α螺旋肽阿拉霉素即為一種螺旋肽，它可以在脂膜間形成電位控制的離子通道。

2. 環(huán)肽:

如：鵝膏毒環(huán)肽（amanitins）、 桿菌肽（bacitracin）、粘菌素（colistin）、cyclotide、多粘菌素（polymyxin）。

3. 含有一個或多個二硫鍵的多肽:

Hepcidin結(jié)構中有一帶有4個二硫鍵的β片層結(jié)構，另一個例子即小的富含半胱氨基的陽離子蛋白，防衛(wèi)素（defensin）, 由18-45個氨基酸組成，其中含有 6 (脊椎動物) - 8個保守半胱氨基。

4. 富含特定氨基酸的多肽:

富含特定氨基酸的多肽：如脯氨酸(如apidaecins)、α-氨基異丁酸（α-aminoisobutyric acid (Aib)）、 半胱氨基等。Myticin是一種新型富含半胱氨基的抗菌肽。

抗菌肽 have biological significance and are promising candidates for novel therapeutic agents. Many peptides are reported to have a wide range of biological activities, including use as polypeptide antibiotics, anti-HIV agents, insecticides, and anti-tumor, anti-fouling, anti-microbial, trypsin inhibition, and uterotonic agents to combat pathogenic microorganisms in human and veterinary medicine.

Some peptide synthesis techniques have been optimized to synthesize specific antimicrobial peptides. The physicochemical parameters of these peptides, such as net charge, helicity, and hydrophobic moment, can be modified during the peptide synthesis process. Other strategies including using D-amino acids, Pro to Lys substitution or fluorinated amino acids for regular amino acid substitution have been found useful in breaking the secondary structure and thus to reducing hydrophobic interactions. Usually, different analytical approaches are used for specific peptide synthesis. Mass spectrometry, such as MALDI-TOF, LC-electrospray ionization (ESI), ion trap MS, and direct-infusion ESI Ion Trap MS, are used to identify products of solid-phase synthesis and thereby optimize synthetic conditions.

Short synthetic peptides can be used as nutritional aids and health foods. Compared to intact-protein diets, free-amino-acid diets, and parenteral nutrition support, peptides have advantage in the stimulation of gut mass, reduction of bacterial translocation, maintenance of gut, improved visceral protein synthesis (versus intact protein), maintenance of hepatic function (versus TPN), and helping facilitate nitrogen absorption, utilization, and tolerance. Recent studies show that bioactive peptides can enhance antioxidant status, antisepsis capacity, immune function, anti-inflammatory capacity, mineral absorption, and appetite.