Isolation of nephrocalcin from kidney tissue of nine vertebrate species

Nephrocalcin (NC), a urinary calcium oxalate monohydrate (COM) crystal growth inhibitor, was purified from kidneys of nine vertebrate species including humans. All isolates were glycoproteins with high contents of aspartic and glutamic acids and small amounts of basic and aromatic amino acids. Carbohydrate contents ranged from 4 to 16 wt% among the different species, but all contained fucose, mannose, galactose, glucose, galactosamine, glucosamine, and N-acetylneuraminic acid. Although amino acid and carbohydrate compositions were similar, dissociation constants derived from calcium oxalate monohydrate inhibition varied between 10(-7) and 10(-8) M, and highest affinity could be related to highest ability of the kidney of origin to concentrate urine. Using an antibody raised against NC from human kidney tissue culture medium, we found strong immunoreactivity with two species, pigs and sheep. Thus far all vertebrate kidneys possess COM growth-inhibiting material that seems to be of glycoprotein character, and all the glycoproteins isolated so far share similar features, suggesting NC-like proteins are a well-conserved trait.