Proteins of the kidney microvillar membrane; analysis by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and crossed immunoelectrophoresis.

A microvillar fraction was prepared from human kidney cortex. This fraction was seven to 10 times enriched in aminopeptidases N and A, gamma-glutamyltransferase, dipeptidyl peptidase IV, neutral endopeptidase and alkaline phosphatase. Dipeptidyl peptidase IV activity of human renal microvilli could be inhibited by di-isopropylphosphorofluoridate and neutral endopeptidase activity by phosphoramidon. Nearly all the activity of aminopeptidases A and N could be removed from the membrane by treatment with papain, but only 19% and 33% of dipeptidyl peptidase IV and gamma-glutamyltransferase activities were released under the same conditions. Neutral endopeptidase and alkaline phosphatase were not solubilized by papain. Treatment with elastase gave results similar to papain, except that gamma-glutamyltransferase was not released. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis under reducing conditions of microvilli revealed 36 polypeptide bands, 12 of which contained carbohydrate. A band of apparent Mr 130 000 was labelled with [3H]di-isopropylphosphorofluoridate and hence identified as dipeptidyl peptidase IV. Antibodies raised to human kidney microvilli produced 11 precipitates with detergent solubilized proteins and six with papain released proteins. Several of the precipitates were identified histochemically. Microvilli prepared from human kidney are very similar to microvilli from pig and rabbit kidney with respect to enzymology, response to papain treatment, sodium dodecyl sulphate-polyacrylamide gel patterns and immunochemistry.