Transient kinetics of ligand binding and role of the C-terminus in the dUTPase from equine infectious anemia virus

Transient kinetics of the equine infectious anemia virus deoxyuridine 5'-tr iphosphate nucleotide hydrolase were characterized by monitoring the fluore scence of the protein, Rate constants for the association and dissociation of substrate and inhibitors were determined and found to be consistent with a one-step mechanism for substrate binding. A C-terminal part of the enzym e presumed to be flexible was removed by limited trypsinolysis. As a result , the activity of the dUTPase was completely quenched, but the rate constan ts and fluorescent signal of the truncated enzyme were affected only to a m inor degree. We conclude that the flexible C-terminus is not a prerequisite for substrate binding, but indispensable for catalysis. (C) 2000 Federatio n of European Biochemical Societies.