Second, the nonpolar side chains of P166, I170 and L230 favor substrate deprotonation to form the enediolate phosphate trianion through either enhancement of stabilizing interactions between the polar amino acid side chains and negative charge at the enediolate oxygen of this reaction intermediate, or through enhancement of the basicity of E165. There is evidence that the changes in ∆G 0 and ∆G ‡ reflect both type of effects: