Glycoprotein calcium oxalate crystal growth inhibitor in urine.

Urine is normally supersaturated with respect to calcium oxalate. Inhibitors of the growth and aggregation of calcium oxalate crystals are present in urine and probably protect against calcium stone formation. These inhibitors are deficient in stone formers. The major inhibitor of calcium oxalate crystal growth is a non-dialyzable, anionic macromolecule. An acidic glycoprotein has been isolated from urine and human kidney tissue culture medium which inhibits calcium oxalate crystal growth in vitro. This glycoprotein crystallization inhibitor has a molecular weight of 14,000 daltons and contains 2-3 residues of gamma-carboxyglutamic acid. The dissociation constant for the calcium oxalate crystal-inhibitor complex is about 10(-7) M. The glycoprotein isolated from the urine of calcium stone formers has a decreased affinity for crystal surface, and a proportionally weaker inhibitory activity; it also lacks gamma-carboxyglutamic acid.