Chemistry
Kinetic Isotope Effects in Enzyme-Catalyzed Proton Transfer Reactions
Quick fact
When a hydrogen in a substrate is replaced by deuterium, an enzyme-catalyzed proton transfer can slow down by a factor of 2 to 10 or more. This large kinetic isotope effect proves that the proton is directly involved in the rate-limiting step and travels through the transition state partially 'in flight' — not just loosely associated.
Why this is interesting
Ever wondered how enzymes make proton transfers happen billions of times faster than simple chemistry allows? Swapping a single hydrogen for its heavier twin, deuterium, can reveal the hidden steps of the reaction.