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Biosynthesis: Procollagen

In order for the organism to develop an extracellular network of collagen fibers, the cells involved in the biosynthetic process must first synthesize a precursor known as procollagen. This molecule is later enzymatically trimmed of its nonhelical ends, giving rise to a collagen molecule that spontaneously assembles into fibers in the extracellular space. Procollagen molecules have been identified as precursors of the three interstitial collagens (Types I, II, and III). Several of the N- and C-terminal peptides (propeptides) have been characterized and the primary sequences determined.

The carboxyterminal propeptides of both pro α1 and pro α2 chains have molecular weights of 30,000 to 35,000 Daltons and globular conformations without any collagen like domain. These peptides contain asparagines-linked oligosaccharide units composed of N-acetylglucosamine and mannose. Once the molecule is completed and translocated to the cell surface, the extensions are enzymatically removed from those collagens, which then form fibrils. Enzymes that selectively remove these extensions can be found in a variety of connective tissues, and in the culture media derived from collagen-secreting cells.

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