The soluble adenosine triphosphatase of Thiobacillus ferrooxidans

Adenosine triphosphatase (ATPase) from Thiobacillus ferrooxidans was purified 55-fold. Polyacrylamide gel electrophoresis of the most purified fraction showed only one major band; histochemical analysis showed that the ATPase activity was associated with this band. The pH optimum is 9-10. The enzyme hydrolyzed ATP stoichiometrically to ADP and inorganic phosphate, the Km for this substrate being 7.75 times 10-3 M. GTP and ITP are alternate substrates, the Km values for these being 6.71 times 10-3 M and 3.12 times 10-3 M, respectively. ADP is slightly hydrolyzed. Magnesium, manganese, and calcium can serve as cofactors; Km values for these are 2.0 times 10-3 M, 9.4 times 10-4 M, and 8.0 times 10-4 M, respectively. The enzyme activity was not activated by either sodium or potassium, but a combination of the two ions were inhibitory. Azide and p-hydroxymercuribenzoate strongly inhibited the enzyme activity, whereas cyanide, dinitrophenol, and N,N'-dicyclohexylcarbodiimide (DCCD) were without effect. The enzyme was cold labile at 0 degrees-C, but was more stable at 18-24 degrees-C.