Turnover Number
The number of substrate molecules converted per catalytic site per unit time.
Formula / equation
TON = molecules converted / active sites
Unit
s⁻¹
In depth
Turnover number measures intrinsic catalytic efficiency independently of how much catalyst is present, allowing fair comparison between catalysts. In enzymology it equals k_cat, the maximum rate divided by the enzyme concentration, and spans an extraordinary range across different enzymes.
Examples in the real world
Carbonic anhydrase reaches 600,000 s⁻¹, while lysozyme manages only about 0.5 s⁻¹.