Some Interrelated Aspects of Proline and Hydroxyproline Metabolism

PROLINE is known to be the sole source of hydroxyproline residues in collagen 1 and is converted to hydroxyproline only after its incorporation into a polypeptide 2,3 . If proline labelled with carbon-14 is employed as a specific precursor of hydroxyproline residues of collagen, the isotope concentration in urinary excretion products derived from such residues should reflect the rate of collagen catabolism. Pyrrole -2-carboxylic acid, an important product of hydroxyproline catabolism 4 , as well as ‘free’ hydroxyproline and ‘bound’ hydroxyproline, was studied in these experiments. The present communication deals with the metabolic interrelationships between these urinary excretion products. For purposes of comparison the metabolic behaviour of proline and hydroxyproline residues of skin collagen is also considered.