The collagen triple helix structure is not found in -

Triple helix formation occurs in endoplasmic reticulum at procollagen level. Triple helix of procollagen is packed into secretory intracellular vesicles in the Golgi-apparatus. These vesicles then secrete the procollagen into extracellular space where it is converted to tropocollagen (collagen monomer). Tropocollagens aggregate into collagen fibrils which intern become extensively cross-linked to form 'collagen fibers'.