Phosphate binding energy and catalysis by small and large molecules.

Area of Science:

• Catalysis
• Enzymology
• Biochemistry

Background:

• Catalyzed reactions achieve rate acceleration by lowering activation energy barriers.
• Transition state binding energy (ΔG‡S) quantifies the stabilization of the reaction's transition state by the catalyst.
• Evaluating ΔG‡S is crucial for understanding all catalytic processes.

Purpose of the Study:

• To evaluate transition state binding energies for catalysis by metal ion complexes and enzymes.
• To compare the catalytic efficiency of small-molecule catalysts with that of enzymes.
• To elucidate the mechanisms by which enzymes achieve high transition state stabilization.

Main Methods:

• Calculated transition state binding energies (ΔG‡S) for metal ion complexes (Zn2+, Eu3+) and enzymes.
• Studied the cleavage of RNA analogue HpPNP catalyzed by Zn2(1)(H2O).
• Investigated enzyme-catalyzed reactions including orotidine 5 -monophosphate decarboxylase, alpha-glycerol phosphate dehydrogenase, and triosephosphate isomerase.

Main Results:

• Zn2(1)(H2O) catalysis of HpPNP cleavage yielded ΔG‡S = -9.6 kcal/mol, with optimal activity at high pH.
• Active catalyst Zn2(1)(H2O) exhibits high affinity for transition state dianions and analogues over phosphate monoanions.
• Enzymes stabilize transition states by ~12 kcal/mol through interactions with non-reacting phosphate groups, exceeding small-molecule catalysts (~10 kcal/mol).

Conclusions:

• Enzyme transition state stabilization via non-reacting substrate fragments is a key factor in their high catalytic efficiency.
• Enzymes may possess a modular design with distinct active sites for reactive fragments and phosphodianion binding.
• This modular design, involving flexible loops and optimized local environments, can be generalized to various enzyme-catalyzed reactions.