Isolation and purification of a new glycoprotein from human urine inhibiting calcium oxalate crystallization

A calcium oxalate crystal growth inhibitor was isolated from human urine using DEAE-Sephacel gel followed by Sephacryl S-300 chromatography and FPLC column. The isolated inhibitor was a uronic-acid-rich protein (UAP). It was found to be a glycoprotein with a molecular weight of 35,000 Da as determined by SDS-polyacrylamide gel electrophoresis. Inhibitory activity was demonstrated using a calcium oxalate crystallization system. In addition UAP, nephrocalcin (NC) or nephrocalcin-like (NC-like) activity was an effective inhibitor in this system. However, the inhibitory activity of UAP appeared to be higher than that of NC or NC-like activity. This finding suggests that NC or NC-like activity is not only urinary protein with strong inhibitory activity. UAP and probably other proteins also play a role in the control of urinary crystal growth.