DUAL ULTRASTRUCTURAL LOCALIZATION OF ACID PHOSPHATASE IN MOUSE KIDNEY TUBULE CELLS

Localization of a membrane-associated acid phosphatase of the tubule epithelial cells of mouse kidney was demonstrated at the fine structural level using a postdiazo coupling technique designed by Smith and Fishman (1969). Enzyme activity appeared in the plasma and infolding membranes and in the lysosomes of epithelial cells of both proximal and distal tubules. Basal infolding membranes were stained most intensely by dense deposits of the enzyme product, which were localized in the outer leaflets. Basement membranes underlying the tubule cells also revealed dense enzyme product. These results were compared with those obtained by Gomori's technique on the same mouse kidney. In this case, lysosomes were positive and infolding and basement membranes were negative. The plasma membrane acid phosphatase is considered to be the morphologic counterpart of microsomal acid phosphatase observed in earlier biochemical studies in our laboratory. Finally, these findings can be interpreted as suggesting separate kidney microsomal and lysosomal isoenzymes of acid phosphatase, each possessing a separate ultrastructural identity.