Enzyme-substrate Complexes

“Enzyme-substrate complex” is a term used to describe the interaction between an enzyme and its substrate in the process of enzyme catalysis.
The substrate is the molecule upon which the enzyme will act. It fits into a region on the enzyme known as the “active site.”
Each enzyme has a unique active site that matches the specific shape of its substrate. This is often referred to as the “lock and key” model due to the precise fit.
The formation of the enzyme-substrate complex is the first step in enzymatic action.
The union of enzyme and substrate at the active site lowers the amount of energy needed for reactions, allowing it to proceed faster. This is known as lowering the activation energy.
The enzyme-substrate complex remains intact until the reaction is complete. The substrate is transformed into one or more products, which are then released.
Once the products are released, the enzyme is free to bind with new substrate molecules. Enzymes are not used up in the reactions they catalyse and can be used again and again.
Environmental factors such as temperature, pH and substrate concentration can affect the rate at which enzyme-substrate complexes are formed and thus the rate of enzyme action.
High temperatures can denature enzymes, changing their active site’s shape and preventing them from forming enzyme-substrate complexes, essentially “losing the key to the lock.”
Similarly, pH levels that are too high or too low can also alter the shape of an enzyme’s active site.
Increasing substrate concentration usually increases the rate of reaction since there are more substrate molecules available to form complexes with the enzyme, until a saturation point where all the active sites are occupied.
An inhibitor is a substance that can bind to an enzyme and reduce its activity. Inhibitors may bind to the active site, blocking substrate access (competitive inhibition), or they may bind to another part of the enzyme, altering the shape of the active site (non-competitive inhibition).