Studies on the Biosynthesis of Collagen Ii. the Conversion of 14c-l-proline to 14c-hydroxyproline by Fowl Osteoblasts in Tissue Culture by R. H. Smith, Ph.d.,* and Sylvia Fitton Jackson, Ph.d

The formation of mature mammalian collagen fibre protein requires the incorporation in peptide linkage of, inter alia, 35 residues per cent of glycine, 12 residues per cent of proline, and 10.5 residues per cent of hydroxyproline. According to our present knowledge, in the animal kingdom hydroxyproline occurs only in the collagenous group of proteins and in elastin, which contains 1.5 residues per cent. Some of the characteristic mechanical, physical, and chemical properties of collagen fibres may be associated, at least in part, with its high content of hydroxyproline (e.g. Gustavson (2)). In spite of the high hydroxyproline content of the collagen fibre protein, it seems that dietary hydroxyproline is not readily utilised by the intact, adult animal in the synthesis of this protein. Stetten (4) fed lSN-labelled (L)-hydroxyproline to intact adult rats and found that the greater part of the 15Nlabelled material was recovered from the urine. Some of the I~N administered was also recovered from the body protein, but the very low isotopic concentration of the isolated hydroxyproline indicated that in 3 days less than 0.1 per cent of the hydroxyproline of these rats had been derived from the dietary hydroxyproline. A higher concentration of I~N was found in the glutamic acid, aspartic acid, and arginine of the body proteins and probably came directly from degradation products of the hydroxyproline. The body proline contained only traces of 15N indicating that little, if any, of the proline of the body was derived from dietary hydroxyproline. In earlier experiments, Stetten and Schoenheimer (5) had shown that 15N-labelled proline fed to intact, adult rats was readily incorporated into body protein, a significant part of the lSN-labelling appearing in the hydroxyproline fraction of the carcass protein in 3 days. On the basis of this work, Stetten (4) wrote . . . "the hydroxyproline of proteins is not derived to any appreciable extent from dietary hydroxyproline, but rather from the oxidation of proline which is already bound, presumably in peptide linkage."