# Changes in Water Dynamics by Osmolytes Regulate Enzyme Activity

## TL;DR

This study shows that osmolytes influence enzyme activity by altering the dynamics of surrounding water molecules.

## Contribution

The paper reveals a direct link between osmolyte-induced changes in water dynamics and enzyme activity.

## Key findings

- Osmolytes that increase water mobility, like urea, enhance enzymatic reactions.
- Osmolytes that restrict water mobility, such as sugars, suppress enzymatic reactions.
- The correlation holds in both binary and ternary systems, indicating indirect enzyme modulation via water dynamics.

## Abstract

Although water is considered to play a crucial role in
biological
functions, the relationship between the water’s molecular dynamics
and enzyme activity has not been systematically clarified. In the
present study, we investigated the effects of osmolytes on enzyme
activity by focusing on the dynamics of the surrounding water. Degradation
of amylose by α-amylase (iodine–starch reaction) was
monitored by visible light absorption to determine reaction rates.
Terahertz time-domain spectroscopy was used to probe the collective
rotational dynamics of water molecules on a picosecond time scale,
allowing us to assess changes in water dynamics caused by osmolytes.
We identified a clear correlation between enzyme activity and water
dynamics beyond the molecular species of osmolytes: osmolytes that
enhanced water mobility, such as urea, accelerated enzymatic reactions,
whereas those that restricted water mobility, including sugars and
polyols, suppressed enzymatic reactions. This correlation was consistently
observed not only for osmolyte–water binary solutions but also
in enzyme–osmolyte–water ternary systems, strongly implying
that osmolytes affect enzyme activity indirectly through modifications
of the surrounding water dynamics. These findings provide experimental
evidence that enzymatic reactions are highly sensitive to picosecond-scale
solvent dynamics. Osmolytes probably function as modulators of enzyme
activity through their hydration effects. By highlighting the central
role of water dynamics in enzymatic catalysis, this study deepens
our understanding of the molecular mechanisms underlying enzyme function
and offers a framework for interpreting osmolyte effects in biological
systems.