4,4'-Diacetyldiphenylurea-bis(guanylhydrazone) (
DDUG), an agent very effective against several animal
leukemias and
tumors, was found, spectrophotometrically, to interact in a biphasic manner with several natural, native and heat-denatured, and synthetic DNAs. The spectrum of
DDUG was shifted towards the visible region with a hypochromic shift reaching a maximum hypochromicity at 316 mmu at a 1 : 1 molar ratio of
DDUG to
DNA nucleotide. Increasing molarity of
DNA nucleotide resulted in a further shift towards the visible end, but with hyperchromicity rather than hypochromicity, and reaching its peak at 323 mmu. The interaction with yeast
RNA was much weaker than that with
DNA. 4,4'-Diacetyldiphenylurea (
DDU) did not show any interaction with
DNA; its monoguanylhydrazone (DDUM) showed only a hypochromic interaction. In contrast to
DDUG,
methylglyoxal-bis( guanylhydrazone (CH3-G), an aliphatic bisguanylhydrazone with antileukemic properties, showed only a hypochromic interaction with
DNA at low ionic strength. Unlike
DDUG, CH3-G was a very weak inhibitor of the
DNA polymerase reaction. The hypochromic shift of the
DDUG spectrum with
DNA was abolished in the presence of 15 mM
sodium citrate or 500 mM NaCl but not in the presence of 150 mM NaCl or 100 mM
sodium acetate. The hyperchromic shift was abolished in the presence of 8 M
urea. From the results obtained with different DNAs,
RNA, synthetic
polynucleotides and
nucleotides, it appears that the total shift of the
DDUG spectrum in the presence of intact
DNA can not be ascribed to interaction with a single base although a greater shift occurred in the presence of G-C rich
DNA.