食品和医疗保健应用：抗菌肽

抗菌肽在生活中无处不在，它们常常是低分子量(2-5 kDa)，有时又被称作防御素，长度通常在12至50个氨基酸之间。根据它们的结构特性，可归为以下4类。

1. 螺旋肽:

α螺旋肽阿拉霉素即为一种螺旋肽，它可以在脂膜间形成电位控制的离子通道。

2. 环肽:

如：鹅膏毒环肽（amanitins）、 杆菌肽（bacitracin）、粘菌素（colistin）、cyclotide、多粘菌素（polymyxin）。

3. 含有一个或多个二硫键的多肽:

Hepcidin结构中有一带有4个二硫键的β片层结构，另一个例子即小的富含半胱氨基的阳离子蛋白，防卫素（defensin）, 由18-45个氨基酸组成，其中含有 6 (脊椎动物) - 8个保守半胱氨基。

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-氨基异丁酸（α-aminoisobutyric acid (Aib)）、 半胱氨基等。Myticin是一种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.