A DFT study of the active role of the phosphate group of an internal aldimine in a transamination reaction.

A transamination reaction from an internal aldimine ([PLP]) and ( S )-alanine to pyridoxamine phosphate (PMP) and pyruvic acid was investigated by DFT calculations. As [PLP], a model where the lysine (-Lys) part was approximated by -CH[-NH-C(O)-CH 3 ]-C(O)-NH-CH 3 was adopted. (H 2 O) 4 was also included to trace reaction paths involving proton transfers. 13 elementary processes were obtained. For (the external aldimine → quinoid), (quinoid → ketimine) and (ketimine → carbinol amine) processes, the water dimer was found to connect a phosphate-group oxygen with the moving proton. The connection promoted the Grotthuss-type proton transfer in transition states. It was revealed that the phosphate group is not a mere substituent but has the central role in the transfer.