Kcat, Catalytic Efficiency Equations

Memory Hack💡

To remember the difference between Kcat and Catalytic Efficiency equations: 

Kcat is how fast one enzyme works when it is fully loaded. 

Catalytic Efficiency is how good the enzyme is when it's actually working in real conditions. 

Notes

Kcat: Vmax/[E] 

[E]= the concentration of enzyme

Kcat is the turnover number or catalytic constant. This number tells us the maximum number of substate molecules that are converted into product by one enzyme over a period of time (typically one second). To put it a little plainer, it is the # of substrate molecules that turn into product per enzyme (per second). 

From here, we can look at catalytic efficiency: Kcat/Km. 

If we think about the factors involved in this equation, this number will take into account how quickly the enzyme converts substate to product, and its affinity for the substrate, aka how well the enzyme binds to it.