Studies on the intracellular localization of collagen synthesis in the intact chick embryo.

The almost unique localization of hydroxyproline in collagen and the availability of methods for the assay of the imino acid offer a convenient approach to studies on this protein. In the experiments described here, L-proline-Cl4 was injected into embryonated eggs, and the specific activities of protein-bound proline and hydroxyprolinei in various subcellular fractions of the embryo were determined. Protein-bound hydroxyproline with the highest specific activity appeared in the microsomal fraction, which suggests that collagen is synthesized by mechanisms imilar to those which have been implicated in the synthesis of other proteins (1).