Isolation and purification of a high molecular weight substance from human urine which inhibits calcium oxalate crystal growth.

Abstract

A high molecular weight inhibitor of calcium oxalate crystal growth in human urine was investigated. Three inhibitors were isolated by DEAE-Sephacel ion-exchange chromatography and, of these, the substance we named "Peak 3 protein" seemed to be the main inhibitor in human urine. Peak 3 protein and several was purified by fast protein liquid chromatography and polyacrylamide gel electrophoresis. This substance, with a molecular weight of 30 kDa, did not contain uronic acid and its inhibitory activity decreased after digestion with proteinase. The difference between Peak 3 protein and several inhibitors previously reported was investigated but no clear difference could be found. The fact that it was the protein structure which was responsible for the inhibitory activity and the fact that Peak 3 protein probably possessed many side-chains which did not contribute to the inhibitory activity influenced the outcome of the investigation.