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Catalytic inhibition of topoisomerase II isozymes by S(−)XK469. ATP-dependent relaxation of superhelical pBR322 DNA is shown for purified human topoisomerase IIβ (Upper) and purified human topoisomerase IIα (Lower). Inhibition was measured by quantitation of the form I band in the ethidium stained gels. The graph from which the IC50 value was determined is shown below each gel. Controls (C) are pBR322 DNA without added enzyme.
