ROLE OF NEPHROCALCIN IN INHIBITION OF CALCIUM-OXALATE CRYSTALLIZATIONAND NEPHROLITHIASIS

Kidney cells produce at least three proteins that slow the rate of cal cium oxalate crystallization. Nephrocalcin (NC), one of the three, is an acidic glycoprotein that contains gamma-carboxyglutamic acid (GLA), and inhibits nucleation, aggregation and growth of calcium oxalate cr ystals. Nephrocalcin is abnormal in urine of stone-forming patients, i n lacking GLA. It acts by adsorbing to crystal surfaces. NC is produce d by cultured renal proximal tubule cells, and by some lines of renal carcinoma cells, but its regulation is not yet characterized. Its sequ ence is not known, nor do we known the molecular basis for the abnorma l character of NC is stone-forming patients. Compared to Tamm-Horsefal l protein and uropontin, the two other inhibitors, NC is very potent, and is probably of major importance in protecting kidneys against supe rsaturations caused by normal water conservation.