Hydroxyproline Metabolism in Type II Hyperprolinaemia

Abstract

Hydroxyproline metabolism was studied in two patients with type II hyperprolinaemia (HP II) using oral loadings of hydroxyproline or hydroxyproline-ornithine. Δ1-pyrroline-3-hydroxy-5-carboxylic acid (3 OH-PC) and Δ1-pyrroline-5-carboxylic acid (PC) were identified in the urine. The urinary excretion of both 3-OH-PC and PC increased in HP II patients but not in healthy controls during oral loading of hydroxyproline and hydroxyproline-ornithine. The plasma level of proline in patients with HP II is very high but the hydroxyproline concentration is normal or only slightly increased. Therefore one can assume that hydroxyproline is converted to pyrrole-2-carboxylic acid, which is excreted in urine as a glycine conjugate. In this study it was demonstrated that the highly elevated plasma level of proline in one of the patients with HP II decreased greatly after hydroxyproline-ornithine load; this change was followed by a 40-fold rise in urinary excretion of proline.