Conformations of protein moieties and chromophore-protein interactions in the antitumor antibiotics, macromomycin and auromomycin, characterized by IR and CD spectral analysis.

The free chromophores (chr) extracted from macromomycin (MCR) and auromomycin (AUR) showed different IR spectra in KBr tablets and different CD spectra in ethanol or methanol solution. Chr-MCR contained a greater amount of alkyl moieties than chr-AUR as shown by much stronger IR absorbance at 2960 cm-1. The IR spectra of MCR, AUR and their apo-proteins (apo) in D2O showed that major parts of the proteins formed antiparallel beta-pleated sheets. Apo-AUR exhibited a faster H-D exchange than AUR, indicating existence of more extensive "nonmotile parts" of the beta-sheet formed through the chromophore-protein interaction in AUR. However, apo-MCR exhibited a slightly faster H-D exchange than MCR. This difference presumably was associated with the lower content of the chromophore (1.4 wt%) in MCR than that in AUR (8.2 wt%). Chr-AUR was extracted from the intact antibiotic with methanol more efficiently than chr-MCR. Further, a marked bathochromic effect by the chromophore-protein interaction was observed in the CD and UV absorption for MCR, but not for AUR. These results indicated that chr-MCR was tightly bound to the protein moiety while most of chr-AUR was loosely bound.