Immunochemical analysis of high molecular mass urinary proteins

Urinary high molecular mass proteins (fraction P) solubilized in Triton X-100 and by papain have been compared with the solubilized human renal brush border membrane proteins. Crossed immunoelectrophoresis of Triton X-100 fraction P extract, by means of two polyspecific antisera directed against either renal membrane or fraction P, revealed eleven immunoprecipitates antigenically identical with detergent renal membrane antigens. Among them, five hydrolases were identified by zymogram staining: microvillus aminopeptidase, maltase, trehalase, gamma-glutamyltransferase and alkaline phosphatase. Eight papain-solubilized fraction P proteins and Triton X-100-solubilized membrane extract presented 'identity' patterns in tandem crossed immunoelectrophoresis, but differed in their amphiphilicity, as demonstrated by the change of precipitation pattern on charge-shift caused immunoelectrophoresis. Among the eleven detergent-solubilized fraction P antigens, nine were proved to be amphiphilic proteins and six presented bidirectional charge shifting properties similar to those of renal membrane antigens. Quantitatively, five detergent fraction P proteins were found in the same amounts as in renal membrane extract, two in lesser amounts and four in greater. Moreover, the same two plasma proteins were identified in fraction P as in the renal membrane. Thus important similarities exist between the urinary fraction P and the native renal membrane.