Intracellular degradation of bleomycin hydrolase in two Chinese hamster cell lines in relation to their peplomycin susceptibility

The Chinese hamster lung (V79) cell was intrinsically 10-times more resistant to peplomycin, a bleomycin-related antitumor antibiotic, than the Chinese hamster ovary (CHO) cell. This may be associated with the 3-times higher levels of recovery of bleomycin hydrolase activity of the V79 cell. The degradation of bleomycin hydrolase molecules in both V79 and CHO cells was examined using a monoclonal antibody specific for the enzyme. Labeling experiments showed that the bleomycin hydrolase in CHO cells was less stable than the comparable enzyme in V79 cells, and that 48 kDa subunits comprising bleomycin hydrolase (a homohexameric enzyme) molecules were degraded into 31 kDa forms in both cell lines. The 105 000 × g pellet (microsomes) fraction obtained after subcellular fractionation of CHO cells contained both 48 kDa subunit and 31 kDa forms of bleomycin hydrolase, while the 105 000 × g supernatant cytosol fraction yielded only 48 kDa subunit forms of the enzyme. Moreover, bleomycin hydrolase activity of both V79 and CHO cells was almost entirely recovered from the cytosol fraction. These results suggest that degradation of the 48 kDa subunit form of bleomycin hydrolase in these two lines of cultured cells into the 31 kDa form occurs on the plasma membrane or the endoplasmic reticulum, with which the resulting large number of bleomycin hydrolase molecules or degradated forms of the enzyme that have lost enzymatic activity are associated.