An effect of magnesium adenosine 5'-triphosphate on the structure of azoferredoxin from Clostridium pasteurianum

Azoferredoxin from $\text{Clostridium}\text{pasteurianum}$ has been treated anaerobically with 65 fold excess of α,α′-dipyridyl in the presence and absence of various nucleotides. Under reduced conditions 1% of the iron of AzoFd is chelated by α,α′-dipyridyl between 1 minute and 1 hour. However, when ATP is added in the presence of Mg²⁺, 80% of the iron in azoferredoxin is chelated within an hour. This effect is reproducible and nonenzymatic. The lack of this effect with other purine and pyrimidine nucleotides demonstrates that it is specific for magnesium ATP. Treatment of azoferredoxin with 4 M urea or oxygen in the presence of α,α′-dipyridyl induces a similar effect. An ATP-induced change in the availability of the iron in azoferredoxin to the chelator, α,α′-dipyridyl, is evidence that a conformational change has occurred.