SCHEME 3.
Schematic representation of the proposed mechanism for the synthesis of cDPG. In step 1, the cDPG 2-phosphate attacks the γ-phosphate of ATP, forming the 2-pyrophosphate intermediate. In the second step, the 3-phosphate attacks the pyrophosphate, releasing inorganic phosphate and forming cDPG. Both reactions are SN2 reactions with simultaneous formation and breaking of the P-O bonds. The highly negatively charged transition states are stabilized by magnesium and positively charged amino acid side chains.