Kidney stone matrix. Differences in acidic protein composition.

Organic matrices from kidney stones of several mineral compositions (calcium oxalate, uric acid, and apatite-struvite) were isolated and found to contain an abundance of acidic amino acids. The calcium oxalate stones contained 50% aspartic and glutamic acid residues while the uric acid stones contained over 65%. The apatite-struvite stones had only 30% of these two amino acid residues and also contained 20% glycine residues. Since the specific amino acid composition differed for stones of different mineral content, it was felt that the organic matrix might play the role of a nucleating agent.