Identification of hemoglobin and two serine proteases in acid extracts of calcium containing kidney stones.

By stepwise extraction of kidney stones, first with 10% acetic acid then 0.1 M EDTA, three pools of protein material have been obtained. The soluble material from the acid extract showed well defined bands when analyzed by sodium dodecyl sulfate (SDS) gel electrophoresis, and amino acid sequence analysis of peptides identified hemoglobin as a common constituent. From one stone neutrophil elastase has been identified along with another serine protease of unknown origin. The second pool of material which was soluble in EDTA showed a smear on SDS gel electrophoresis while the third pool consisted of the insoluble matrix. The finding of proteolytic enzymes opens up the possibility that limited proteolysis might be involved in the stone forming process.