THE HARD-SOFT ACID-BASE PRINCIPLE IN ENZYMATIC CATALYSIS - DUAL REACTIVITY OF PHOSPHOENOLPYRUVATE

In this paper, the chemical reactivity of C3 of phosphoenolpyruvate (P EP) has been analyzed in terms of density functional theory quantified through quantum chemistry calculations. PEP is involved in a number o f important enzgmatic reactions, in which its C3 atom behaves like a b ase. In three different enzymatic reactions analyzed here, C3 sometime s behaves like a soft base and sometimes behaves like a hard base in t erms of the hard-soft acid-base principle. This dual nature of C3 of P EP was found to be related to the conformational change of the molecul e. This leads to a testable hypothesis: that PER adopts particular con formations in the enzyme-substrate complexes of different PEP-using en zymes, and that the enzymes control the reactivity through controlling the dihedral angle between the carboxylate and the C=C double bond of PEP.