Peptide

A peptide refers to a compound obtained by dehydration condensation of two or more amino acids. The simplest peptide consists of two amino acids called dipeptides. A peptide containing a plurality of amino acids is called a polypeptide. A polypeptide containing more than 50 amino acids, commonly referred to as a protein. Peptides are widely found in animals, plants and microorganisms. They have important physiological functions and have special functions in biological growth and development, cell differentiation, brain activity, tumor pathology, immune defense, reproductive control and anti-aging. For example, glutathione is a coenzyme of certain enzymes and plays an important role in the redox process in the body. Many hormones belong to peptides, such as oxytocin, vasopressin, glucagon, and adrenocorticotropic hormone, which regulate body metabolism. Hormone regulators secreted by the hypothalamus are also polypeptides that control the activity of hormones released by other endocrine glands. In recent years, enkephalin (pentapeptide) found in the brains of higher animals has an analgesic effect. Many antibiotics produced by microorganisms, such as polymyxin and gramicidin, are peptides and have strong antibacterial effects. A polypeptide refers to a long chain of many amino acid units interconnected by peptide bonds. There are no strict boundaries between peptides and proteins. Generally, a polypeptide containing only tens or fewer amino acid units is called a peptide, and a polypeptide having a relatively large number of amino acid units is called a protein. The amino acid units in a polypeptide are often referred to as amino acid residues because these units have lost a portion of the molecule when they are linked to each other, rather than a complete amino acid. Only amino acid residues at both ends of the peptide chain contain a free alpha-amino group or a free alpha-carboxyl group. The terminal residue having a free α-amino group is called an amino terminal (or N terminal) residue, and the terminal residue having a free α-carboxy group is called a carboxy terminal (or C terminal) residue. The peptides are named in the order from the N-terminus to the C-terminus, and are also written in this order. For example, the pentapeptide of Ser Gly·Try·Ala·Leu contains 5 amino acid residues and 4 peptide bonds called serine glycyl tyrosyl alanyl leucine. Peptides are widely found in animal and plant tissues, many of which have special functions in organisms, collectively referred to as bioactive peptides. In recent years, it has been found that almost all major theories of life sciences, such as immune defense, reproductive control, tumor lesions, anti-aging and anti-aging, involve related active peptides. These theoretical problems are closely related to clinical medical practice, so bioactive peptides are also of great significance in practical applications. There are many types of bioactive peptides. For example, the adrenocorticotropic hormone that stimulates adrenal cortex development is a 39-peptide, and the oxytocin that causes uterine contraction is a nonapeptide, and two important enkephalins having morphine activity are pentapeptides. Many antibiotics are also peptides. Another example is that growth factors are controlled by genes and regulate and control during cell development. Such important substances are polypeptides. The epidermal growth factor contains 50 amino acid residues and the nerve growth factor consists of 118 amino acid residues.