Interaction of formycin A-5'-triphosphate with pyruvate carboxylase

Formycin triphosphate (FTP), a fluorescent analogue of ATP, is a competitive inhibitor of chicken liver pyruvate carboxylase with respect to ATP. The chicken liver Enzyme is unable to utilise FTP as a substrate at a measureable rate, but FTP is a poor substrate for the sheep liver Enzyme. When FTP binds to the Enzyme, its fluorescence is enhanced and in this way the formation of enzyme-FTP complexes can be monitored. Using this property of FTP, the effect of Mg2+ and acetyl-CoA on the binding of nucleoside triphosphates to the chicken liver Enzyme was examined. Mg2+ was found to enhance the binding of FTP whilst acetyl-CoA reduced the fluorescence intensity of a mixture of Mg2+, Enzyme and FTP. Most probably, this was caused by a conformational change in the Enzyme which changed the environment of the fluorophore.