Strong binding of ditrisarubicin B to DNA.

Abstract
DNA binding characteristics of ditrisarubicin B were studied by the fluorescence titration technique. Ditrisarubicin B bound to calf thymus DNA with an affinity higher than any we have ever seen among anthracyclines. The apparent association constant (Kapp) of ditrisarubicin B was 2.36 .times. 108 M-1, which is 22.7 times larger than that of doxorubicin. The apparent number of binding sites (napp) of ditrisarubicin B per nucleotide of DNA was 0.164, and this value is identical with that of doxorubicin. Betaclamycin A, which has a trisaccharide chain at C-7 but no carbohydrate at C-10 in the aglycone, interacted with DNA to give a Kapp of 5.92 .times. 106 M-1 and napp of 0.178. These results suggest to us that the high affinity of ditrisarubicin B for DNA is caused by the existence of a glycosidic chain at C-10.

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