Quantification of neutral cysteine protease bleomycin hydrolase and its localization in rat tissues.

A neutral cysteine protease, bleomycin hydrolase (BH), was found to be present in the range 3.7-131.1 ng per mg of rat tissues by enzyme-lined immunosorbent assay (ELISA). Newborn rat skin contained the highest amount of BH, and relatively high levels of BH were detected in the kidney and liver of 6-week-old male rats. The tissue distribution of BH in female rats was similar to that in male rats. Moreover, BH was detected in the extracts of erythrocytes and leukocyte-rich cells as well as in those of rat hemo-lymphocytic lineage cell lines by Western blotting. The BH level was increased at 6 weeks after birth and then slightly decreased. By immunohistochemistry, BH was localized as granular staining in the distal and proximal tubular cells of the kidney, and it was also detected in hepatocytes of the liver, in the red pulpy region of the spleen and in neurons of the brain. An immunoelectron microscopic study showed that BH-immunoreactivity was essentially located in the cytoplasm and at the outer membrane of the rough endoplasmic reticulum of epithelial cells of the kidney, as well as in that of hepatocytes of the liver. These results suggest that BH may play ubiquitous and unique roles in rat tissues.