For all the N-terminal histidyl peptides tested the catalytic performance was not significantly affected by the identity of the adjacent amino acid residue (Figure ). His-Lys marginally outperforms the other histidyl peptides by the advent of the third cycle although this is not substantial. Potentially, this is due to the additional positive charge from the Lys residue which aids the phosphate transfer to glycerol by electrostatically stabilising the transition state -although further mechanistic studies are required to determine this for certain.