Possible Pol Β Reaction Pathways

Possible nucleotidyl-transfer reaction pathways identified in pol β. (a) Scheme 1, with arrows showing direct deprotonation of the terminal primer O3'H to O2α of the incoming dCTP in conjunction with nucleophilic attack at the Pα center. (b) Scheme 2, direct deprotonation of the terminal primer O3'H to active site Asp residues, in conjunction with nucleophilic attack at the Pα center. (c) Scheme 3, with arrows showing proton transfer steps from the terminal primer O3'H to pyrophosphate, via active site water and D190, in conjunction with nucleophilic attack at the Pα center.

Reference:
Alberts IL, Wang Y, Schlick T., "DNA polymerase β catalysis: are different mechanisms possible?" J Am Chem Soc. 2007, 129(36):11100-10.