Collagen, derived from Greek, means "the product of gum formation". In 1893, the Oxford Dictionary defined collagen as "the constituent of connective tissue that produces colloid when boiled". Later, gross (1956) first named procollagen as the protein monomer of collagen fiber. Now the scientific definition of collagen is: "extracellular matrix (EMC) structural protein, there should be at least one domain in the molecule with three strands of helix conformation composed of α chain (collagen domain).". Collagen is a white, transparent, unbranched fibril with four levels of structure. The monomer of collagen is pro-collagen. The pro-collagen molecule is a long and thin triple helix chain, with a diameter of 15 ℃ and a length of 280 ℃ measured by electron microscopy. It has a rod-shaped structure and a molecular weight of nearly 300000. The specific amino acid sequence on the α chain of type Ⅰ collagen constitutes its primary structure; the secondary structure refers to the formation of collagen specific and tight left-hand helix on the α chain due to the presence of glycine proline? Three peptides; and the existence of glycine in the three peptide cycle makes the three left-hand helices bend around each other to form a tight right-hand composite helix, which is the three level structure of collagen; four The first-order structure generally refers to the formation of stable and strong fibrils by supramolecular aggregation of procollagen molecules in a "quarter staggered" manner. For a long time, collagen has been regarded as a kind of molecule. In fact, collagen contains a wide range of molecules, whose main structure is the same triple helix configuration. Until the 1970s, people gradually realized the diversity of collagen in different tissues. So far, 18 types of collagen have been defined, including 32 polypeptide chains with their own genetic characteristics. Their distribution in tissues has certain tissue specificity, for example, tendon mainly contains type I collagen; cartilage mainly contains type II collagen, while vascular wall, skin and the interstitial of various soft tissues or organs contain type I collagen and type III collagen at the same time, but in different organs, the proportion of the two collagen contents is different. As type I collagen accounts for 90% of the total collagen in organism, the research on type I collagen is the most extensive.
Collagen is the most widely distributed protein in animals, mainly distributed in the connective tissue. It is very important for the formation of animal and human skin, blood vessels, bones, teeth and cartilage, and it is the main material basis of these connective tissues. 70% of the total weight of the skin is collagen, almost all of the cartilage is collagen, and 80% of the normal bone also contains collagen (in the bone, the function of collagen is mainly to use its network structure to stick calcium, phosphorus, minerals and other components to form bone). In recent years, Japan is the first country to supplement collagen in the way of eating. These products can supplement the lost collagen in the human body by oral way, which can be used as the raw material for the synthesis of collagen in the human body, and can enhance the immune function of the human body while providing the beauty effect. But not all so-called collagen has such an effect. In order to achieve oral collagen supplement, the form of collagen intake must be collagen peptide in small molecular state, and the molecular weight of 3000-5000 Dalton that is confirmed to be the most easily absorbed and utilized by human body at present.
