[Localization of glycylproline dipeptidyl aminopeptidase in the liver tissue and possible mechanism of its release into blood flow].

We examined the localization of glycylproline dipeptidyl aminopeptidase (GPDAP) in the liver tissue and the mechanism of its release into blood flow. An immunohistochemical study using rabbit polyclonal antibody against the purified GPDAP from human liver obtained at autopsy was performed in liver biopsy samples with the peroxidase-antiperoxidase stain technique. GPDAP staining was detected on the liver cell membrane around bile canaliculi. After treatment with deoxycholic acid (DOC) or Triton X-100, this enzyme disappeared. GPDAP was solubilized rapidly from microsome of human liver by treatment with either DOC or Triton X-100. DOC or Triton X-100 solubilized GPDAP coincided with the isozyme that was the specific isozyme in sera of patients with acute hepatitis or obstructive jaundice. These results suggest that GPDAP localizes on the liver cell membrane around bile canaliculi and that this enzyme is released by the detergent action of bile acids.