Determination of hydroxyproline in tissues and the evaluation of the collagen content of the tissues

The concentrations of hydroxyproline (an amino acid specific of collagen) in a number of connective tissues were determined. Two procedures were compared. In one of them, amino acids were preseparated by chromatography and then determined on a standard amino acid analyzer. In the other procedure, hydroxyproline was selectively oxidized without amino acid separation and determined by a spectrophotometric reaction with Ehrlich's reagent. Data obtained for purified collagen preparations in accordance with the two procedures were consistent with each other. The results can be somewhat different in unpurified preparations and tissues because of the presence of polysaccharide components in the tissues.