Chemistry
The Kinetic Isotope Effect in Enzyme-Catalyzed Reactions
Quick fact
Replacing a hydrogen atom with deuterium can slow an enzyme-catalyzed reaction by up to 6-10 times, directly revealing that breaking the C-H bond is the rate-limiting step.
Why this is interesting
If enzymes are such perfect catalysts, why does swapping a single atom for a heavier twin slow them down—and why is that slowdown a goldmine for biochemists?