Urinary Hydroxyproline as an Index of Collagen Turnover in Bone

HYDROXYPROLINE, a nonessential imino acid, occurs in the body almost exclusively in collagen, where it accounts for 13 per cent of the total amino acids.1 Man excretes hydroxyproline in the urine in bound and free forms.2 , 3 The free state of the imino acid accounts for less than 4 per cent of the total amount excreted. Bound hydroxyproline, presumably in a polypeptide, is released by acid hydrolysis and accounts for nearly all the urinary excretion of hydroxyproline.2 , 3 A peptide-containing hydroxyproline has been isolated from human urine.4 Guinea pigs with osteolathyrism, a disorder of bone and collagen, excrete increased quantities of hydroxyproline . . .