Quantitative histochemistry of the lysosomal dipeptidyl aminopeptidase II in the proximal tubule of the rat kidney.

The activity of the lysosomal dipeptidyl aminopeptidase II (DAP II) was measured by quantitative histochemical methods in the S1/S2 segments of the proximal tubule using freeze dried and celloidin mounted cryostat sections (FDC sections) of rat kidney. The methodological studies show that there is a linear relationship between the amount of reaction product and reaction time for the first 5 min, as well as section thickness between 4 and 10 microns. Maximal DAP II activities were demonstrated at pH 5.5. The Km of DAP II was about 2.3 mM. In addition to the methodological studies, DAP II activity was also measured in the proximal tubule (S1/S2 segments) of experimental animals (sham-operated and castrated male and female rats). Sham-operated females showed significantly higher DAP II activities than males. DAP II activity increased significantly in castrated males so that there were no significant differences between castrated males, sham-operated and castrated females. The quantitative histochemical results are largely in agreement with biochemical data published earlier.