# Enzyme kinetics at the molecular level

## TL;DR

This paper reviews how enzyme kinetics at the molecular level deviate from the classical Michaelis-Menten equation due to fluctuations and correlations, revealing a regime where the traditional model fails.

## Contribution

It introduces new statistical measures to identify regimes where enzyme kinetics deviate from classical models at the molecular scale.

## Key findings

- Fluctuations cause deviations from MM at the molecular level.
- A regime with temporal correlations violates the MM equation.
- Classical MM validity is limited to bulk, negligible-fluctuation conditions.

## Abstract

The celebrated Michaelis-Menten (MM) expression provides a fundamental relation between the rate of enzyme catalysis and substrate concentration. The validity of this classical expression is, however, restricted to macroscopic amounts of enzymes and substrates and, thus, to processes with negligible fluctuations. Recent experiments have measured fluctuations in the catalytic rate to reveal that the MM equation, though valid for bulk amounts, is not obeyed at the molecular level. In this mini-review, we show how new statistical measures of fluctuations in the catalytic rate identify a regime in which the MM equation is always violated. This regime, characterized by temporal correlations between enzymatic turnovers, is absent for a single enzyme and unobservably short in the classical limit.