Allosteric regulation of eukaryotic initiation factor eIF-2B by adenine nucleotides

Previous studies have shown that eIF-2B purified from rabbit reticulocytes binds ATP and that the binding is prevented by NADP⁺. Because NADP⁺ inhibits the activity of eIF-2B in and vitro reactions we have examined whether or not the activity of eIF-2B is modulated by ATP. In these studies, eIF-2B, purified from rat liver, was incubated with ATP prior to assay. We found that the activity of eIF-2B was inhibited with an IC₅₀ of approximately 0.8 mM. The inhibition was not due to phosphorylation of the factor. However, the inhibition of eIF-2B activity caused by ATP could be prevented by coincubation with either NADPH or fructose-1,6-bisphosphate. The activity of eIF-2B was also inhibited following addition of either ATP or AMPPNP to a post-mitochondrial supernatant prepared from rat liver. Therefore, it is possible that the activity of eIF-2B might be allosterically regulated in vivo not only by changes in the redox slate of pyridine dinucleotides but also by changes in the relative amounts of NADPH and ATP.