Peptide inhibitors of calcium phosphate precipitation in the urine of normal and stone-forming men

Abstract

Peptide fractions from normal and stone-forming human urines were isolated by ion-exchange and gel filtration and the ability of these fractions to inhibit the homogeneous nucleation of calcium phosphate from aqueous solution was examined, using a new quantitative precipitation test. Comparisons between urines from 8 normal male adults and 8 patients with frequently recurring, calcium-containing renal stones revealed a lower mean inhibitory activity in the stone-forming urines than in normal urine but there was a considerable overlap of values and the difference was significant only at the 5% level. No inhibitory activity could be demonstrated in normal or stone-forming urine when calcium oxalate was substituted for calcium phosphate in the precipitation test. The evidence for the existence of urinary inhibitors of calcium salt precipitation was examined and it was concluded that the absence of peptide inhibitors of homogeneous nucleation was not a primary cause of stone formation in our patients.