Studies on the mechanism of action of 6-mercaptopurine. Interaction with copper and xanthine oxidase

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Abstract
Interaction between 6-mercaptopurine [an antineoplastic, immunosuppressive and antiinflammatory agent], Cu2+ and the enzyme xanthine oxidase (EC 1.2.3.2) was examined. Cu2+ inhibited the enzyme: 6-mercaptopurine protected and reversed the enzyme inhibition produced by the metal ion. The formation of a complex between 6-mercaptopurine and Cu2+ seems to be responsible for the observed effect. Job''s method showed the composition of the complex to be 1:1. The apparent stability constant (log K value), as determined by Subhrama Rao and Raghave Rao''s method was 6.74. The formation of a stable complex between 6-mercaptopurine molecules and Cu2+ may be an additional mechanism of action of 6-mercaptopurine, particularly with reference to its antiinflammatory properties [in vertebrates].