The free chromophores isolated from the antitumor
protein antibiotics,
auromomycin (AUR) and macromomycin (MCR), were rapidly inactivated by incubation in serum-containing medium at 37 degrees C in the dark with respect to cytocidal activity to human lung
carcinoma A549 cells. Under the same conditions, the intact
antibiotics, their
pronase-hydrolysates and reconstituents from the chromophores and apo-
proteins were stable. Intact and reconstituted AUR and MCR were more resistant to
pronase digestion than the apo-
proteins. The analyses of the
pronase-hydrolysates of AUR and MCR by SDS-
polyacrylamide gel electrophoresis and ultrafiltration showed that the
antibiotics (13 kilodaltons (kDa] were degraded to produce
peptide fragments (1-3 kDa) in which most cytotoxicity of the
pronase-hydrolysates resided. The
pronase-hydrolysates exhibited a differential cytocidal activity to normal diploid fibroblasts (WI38), their SV40-transformants (VA13) and
carcinoma cells (A549) of human lung origin as was observed for the intact
antibiotics. These results indicate that specific interaction between the chromophores and the
pronase-resistant
peptide segments (1-3 kDa) of the
protein moiety stabilizes the cytocidal activity of the chromophores and also protects the
peptide segments from
pronase digestion.