Catalytic inhibition of DNA topoisomerase II alpha by sodium azide

It has been demonstrated previously that sodium azide reduces the clastogen icity of several DNA topoisomerase II (topo II) poisons in cultured mammali an cells. These studies suggested that azide may be a catalytic topo II inh ibitor. Azide interferes with mitochondrial production of ATP and is also k nown to inhibit cellular ATPases. Since topo II requires ATP for catalytic activity (enzyme turnover), it seemed likely that interference with ATP lev els or ATP catabolism was the underlying mechanism of topo II inactivation; however, this has not been examined in living cells under conditions where the endogenous topo II is active on genomic DNA. The present studies were carried out to verify that azide inhibits endogenous topo II in cells. We s how that azide blocks both decatenation and relaxation activity of purified topo II in a concentration dependent manner and reduces topoII/DNA covalen t complex formation in cells. From these studies, it is concluded that sodi um azide catalytically inactivates topo II via an ATP-sensitive process. (C ) 2001 Elsevier Science Ireland Ltd. All rights reserved.