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Research

Overview: Enzyme Mechanisms, Transition States and KIEs

The realization, over 50 years ago now, that enzymes catalyze reactions by stabilizing the transition state (TS) was a stunningly simple and powerful idea that is still the guiding concept that underpins our understanding of catalysis.

Enzymes catalyze reactions by specifically binding to and stabilizing the TS in preference to any other species. By stabilizing the TS, it reduces the activation energy, accelerating the reaction. Enzymes typically bind substrates & products weakly, with dissociation constants (K_d's) around 10^-3 to 10^-6 M, compared with K_d's as low as 10^-26 M for enzyme-TS complexes.

Our goal is to understand enzyme mechanisms by determining TS structures using kinetic isotope effects (KIEs). TS structures show how enzymes catalyze their reactions.

Determining TS structures at high resolution using KIEs has only become regularly achievable in the last 15 years. This is a tremendous advance, allowing the structures of species that exist for less than a single bond vibration, ~10^-13 s, to be determined with a resolution similar to x-ray crystallography of stable molecules.

Designing Inhibitors as Drugs

Once we know the TS structure for an enzymatic reaction, we can design inhibitors. Stable molecules that closely mimic the charge and shape of the TS will be potent inhibitors that have the potential to be drugs - e.g., as antibiotics or in cancer therapy. By docking the experimental TS structure into the active site of the x-ray structure of the enzyme, we can understand how the enzyme catalyzes the reaction, and therefore how to inhibit it.