Michaelis constant (Km)
Japanese: Km値（ミカエリス定数）
A value indicating the affinity between enzyme and substrate. The smaller the Km, the more efficiently the enzyme works with low substrate concentrations.
The Michaelis constant (Km) is the substrate concentration at which reaction velocity reaches half of Vmax. Derived by Michaelis and Menten in 1913, it is the most fundamental parameter in enzyme kinetics.
An enzyme with a small Km catalyzes reactions efficiently even at low substrate concentrations—meaning high affinity for its substrate. Whether protease continues generating umami in late-stage miso aging, when substrate (protein) has diminished, depends on its Km.
In industrial enzyme selection, Km is a critical criterion. When optimizing fermentation at the molecular level, Km tells us 'how avidly an enzyme captures its substrate.' Where fermentation meets science, new discoveries await.