Characterization of proteolytic systems in human and rat urine

Activities of proteolytic enzymes were detected in rat and human urine by using [125 l] iodo-insulin B chain as a substrate. The pH optimum of human urine activity was in the acidic range (pH 2.0) whereas the rat urine had two pH optima, one at the acidic range similar to human urine and another at pH 7.5. The activities were linear with time and amount of enzyme. Study with various proteinase inhibitors revealed that the acidic pH activities of human and rat urine were apparently of carboxyl endopeptidases since they were totally inhibited by pepstatin 10-8M. The neutral pH proteolysis of rat urine was inhibited by chelating agents and therefore it was considered as a metalloendopeptidase activity. These findings show the difference between the content of urinary proteolytic enzymes in humans and in rats by using a sensitive and simple radioactive assay.