Procollagen I (PCI)

In addition to the typical type I collagen, there is evidence of a type I alpha1-homotrimer collagen consisting of three alpha1(I) chains (Jimenez et al. 1977). 

The carboxyterminal propeptide of type I procollagen (PICP) and the aminoterminal propeptide of type I procollagen (PINP) are enzymatically removed from the procollagen molecule by specific proteases. PICP and PINP are indicators of the synthesis of type I collagen. Cleavage of PICP is required for the initiation of fibril formation, whereas PINP may be retained in the collagen molecule resulting in type I pN-collagen. The retention of PINP is transient, unlike the presence of IIIpN-collagen, and has been considered to regulate fibril diameter (Fleischmajer et al. 1985).