Figure 1

Push mechanism” catalytic amino acid residues. Amino acid residues making up the “push” mechanism within the active sites of SK (A) and AK1 (B). Shown are the protein backbone carbonyl associated with the C6-NH₂, the Thr associated with the proton transfer from C8H to the α-PO₄ (SK, Thr17; AK1, Thr 23), the Arg associated with C8 protonation (SK, Arg110: AK1; Arg128), the Arg coordinated to the α-PO₄ and β-PO₄ (SK, Arg117; AK1, Arg132), Lys associated with the γ-PO₄ protonation (SK, Lys15; AK1; Lys21). The adenylate kinases have two nucleotide binding sites and the equivalent amino acid residues in the second AK1 binding site are carbonyl associated with the C6-NH₂, the Thr associated with the proton transfer from C8H to the α-PO₄ (Thr 39), the Arg associated with C8 protonation (Arg97), the Arg coordinated to the α-PO₄ and β-PO₄ (Arg44/138), Lys associated with the γ-PO₄ protonation (Lys21).