Analytical and Spectroscopic Tools for Studying Enzyme Transition States

Abstract

Enzyme transition states are central to catalysis but remain among the most difficult species to characterize, owing to their high energy, ultrashort lifetimes, and vanishingly small populations. Because they cannot be directly observed, their structural and electronic features must be inferred through a combination of advanced kinetic, spectroscopic, and structural methods. This review provides a concise overview of the principal experimental strategies for kinetics and mixing technologies, and the spectroscopies employed to probe transition states and short-lived intermediates in enzymatic reactions. We dedicate a higher focus on cryogenic techniques and phototriggering methods. Particular emphasis is placed on the complementarity between these approaches where time-resolved methods provide kinetic resolution, cryogenic trapping provides spectroscopic depth, and photocaging provides temporal precision. These strategies not only are powerful tools for mechanistic enzymology but also define the structural and kinetic parameters that govern the rational design of enzyme-based analytical platforms, including biosensors, where transition-state properties set fundamental limits on response time, selectivity, and sensitivity.