Abstract
Differences in the localization of leucine aminopeptidase in the cortex of the rat kidney have been reported with two methods employing the same substrate. Test tube and tissue experiments were carried out in an effort to explain the disparity. Substrate concentration, pH, buffer, the use of an activator, duration of incubation and temperature of incubation were found to have insignificant effects. Four important findings were (1) leucine aminopeptidase activity of the inner cortex of the rat kidney assayed two to three times greater than that of the outer cortex, (2) this difference was confirmed by histochemical demonstration with both methods, (3) fast blue B inhibited the enzyme more than fast garnet GBC and fast Corinth V, and (4) fast blue B coupled faster than the other diazonium salts.