Figure 6.

Free energy profile for the reaction of a whole phosphorylated substrate S-PO₃²⁻ catalyzed by an enzyme that exists predominantly in a stable inactive open form E_O. For simplicity, the Figure shows only the binding energy of the phosphodianion portion of the substrate, ΔG_Pi. The relative small observed binding energy of the phosphodianion group (ΔG_obsd) is the sum of the much larger total available binding energy of this group (ΔG_Pi) and the binding energy that is utilized to drive the unfavorable enzyme conformational change (ΔG_C). Catalysis occurs at a higher energy active closed form E_C, which is stabilized by interactions with the phosphodianion group of substrate at the E_C•S-PO₃²⁻ Michaelis complex (upper profile). In the case that the phosphodianion binding energy is not used to drive the unfavorable conformational change at the ground state Michaelis complex (lower profile), the activation barrier ΔG^‡_chem for turnover of the enzyme-bound substrate will increase by an amount ΔG_C (see text).