There are now at least 15 known collagen types composed of at least 24 chains, (107) and they tend to occur in different tissue as follows.
Type I collagen
Type I of collagen the archetyal collagen, is the most abundant form in the body, constituting greater than 95% of the organic matrix of bone and tendon and 80% of adult skin. It is a major constituent of the cornea, ligaments, sclerae, heart valves and the annulus fibrous of the inter vertebral disc and it also a significant component of blood vessel walls, the lung parenchyma gut, joint capsule, foetal membrane and it is also found in virtually connective tissue matrices.
Type II collagen
Type II collagen is a Homo polymer of a (11) chains, which are as the same size as homologous a. (1) Type II thus has a similar molecular structure to type 1 collagen, type II is found only in hyaline cartilage, intervertebral discs and the vitreous complex network. (112)
Type III collagen
Type III of collagen was first identified as a significant component of foetal skin blood vessel walls and leiomyomas. (113) Type III of collagen has a similar tissue distribution as stimulated in adult skin. (114)
Type I V
Type IV of collagen is a major component of the basement membrane in the dermal-epidermal function to which basal keratin ocytes attach preferentially. It is also produced by endothelial cells and forms on essential element of the micro vascular wall. (108) The molecular consists of three collagen chains with an apparent molecular weight of 140 kilo Dalton.(114)
Type V of collagen is ubiquitous and interfaces between the cell surface and the surrounding matrix. It has a chain length similar to that of the interstitial collagen, and it does not contain any disulphide bonds.
Type VI of collagen is a heterotrimer composed of three different a- chains, which usually have large globular domains at the ends of the polypeptides, it has a high cysteine content and is highly disulphide bonded, with short chains .(108) Type V is the product of fibroblasts and smooth muscle cells and is found in virtually all interstitial connective tissues particularly the skin , the aortic media and cartilage . (115)
Type VII collagen
Type VII of collagen is a homopolymer containing a chains with a molecular light of approximately 170 kilo Dalton giving a triple –helical domain about triple sequence. (116)
Type VIII of collagen was originally identified as a product of endothelial cell cultures. It is a homopolymer with a sub unit molecular weight of 177 kilo Dalton .(117)
Several low molecular weight collagen peptides have recently been isolated from propteolytic digests of cartilage materials from the chick pig and cow.
Type X of collagen is another short chain collagen identified in cartilaginous tissues and chondrocyte cultures is a non disulphide bonded trimmer of polypeptide chains with A molecular weight of 59 kilo Dalton. (118)