Type III collagen is synthesized by fibroblasts, smooth muscle cells, and other cells that produce connective tissue. The initial form, procollagen, undergoes a series of enzymatic modifications both intra- and extracellularly. These modifications include hydroxylation of proline and lysine residues and glycosylation. Once secreted into the extracellular space, procollagen molecules align and form fibrils that are eventually cross-linked to form mature collagen fibers.
