Collagen type III is synthesized as a homo-trimeric pro-collagen comprising three identical pro-alpha(III)-chains. It has been reported that procollagen type III is processed extracellularly at the ECM and can be found by immunostaining intracellular as well as extracellular. Collagens consist of a family of highly specialized glycoproteins of which at least 16 genetically distinct types are known to date. The basal unit of a collagen molecule consists of a triple-helical structure formed by 3 alpha-chains. Predominant amino acids are glycine, proline and hydroxproline. Regularly also lysines and hydroxylysines occur, which are responsible for cross-linkage and glycosylation of the protein chains. Different composition of alpha-chains and different glycosylation contribute to the high variability of collagens in different tissues and organs. Human and bovine procollagen type III (PIIIP) 100%; human and bovine procollagen type and collagen type I <0.1% in RIA at 1:200 dilution..