According to my chemistry book, there are 3 simplified steps within an enzyme catalysed reaction:
- S + E → ES
- ES → EP
- EP → E + P
Where S is substrate, E is enzyme, ES is enzyme substrate complex, EP is enzyme product complex and P is product.
It is my understanding that at first, when substrate concentration is low the rate determining step is step 1, as this is the slowest step in the mechanism.
When you increase substrate concentration to a certain level, where there are no free enzymes remaining to bond with them, adding more substrate will not make the reaction faster, so the order has become 0 with respect to substrate conc.
Is the rate determining step now 2 or 3? I thought it would be 3 as that is the step that frees up more enzymes which could go on to catalyse more reactions. My book says that it is step 2, as "it depends on how fast the ES can convert into EP". But surely this step won't free up more enzymes to catalyse reaction further?
Is the book correct? Can anyone help me understand this?