Conservative substitution of the invariant lysine by arginine abolished ATP hydrolysis but nucleotide-binding activity was retained. From nuclear magnetic resonance (NMR) analyses carried out with adenylate kinase of E. coli it was suggested that the corresponding (Walker A) lysine residue functions in orienting the triphosphate chain of MgATP to a proper conformation
required for catalysis and, in turn, ensures interaction of the substrate with the active site residues. A mutation to arginine interferes with these activities due to a localized conformational change.