Structural and topological homology between porcine intestinal and renal brush border aminopeptidase

Abstract

A method for the preparation of closed, right-side-out vesicles from the brush border membrane of the kidney proximal tubules is described. The aminopeptidase known to be bound to this membrane was investigated in order to compare its properties with those already reported for the intestinal enzyme. Both are composed of a hydrophilic, catalytically active part lying on the external side of the membrane and a short hydrophobic domain probably located in the N-terminal region of one of the subunits ensuring fixation to the lipid matrix. The enzyme were also found to be clinically similar. Moreover, a quantitative immunological technique showed that they contained 6 cross-reacting determinants, consistent with a very high degree of homology. Four of these determinants were accessible in the bound form of the enzymes in the region of the active site. The other two, probably related to the junction between the hydrophilic moiety and the hydrophobic anchor were completely masked in the bound form. The remainder (6 in the intestinal and 4 in the renal enzyme), were heterologous. The accessibility of two well determinants in this latter group was substantially reduced, perhaps by the proximity of the lipid and/or of other enzyme molecules.