Enzyme Substrate Complex

Before discussing the complex itself, we must first understand what an enzyme actually is. Enzymes are a naturally occurring chemical substance, usually a protein that acts as a catalyst for a chemical reaction. Enzymes differ in several ways from other naturally occurring chemical catalysts. They have higher rates and different conditions of reactions. They also have a greater reaction specificity and regulation capacity. Every enzyme has a distinct substrate (surface where or material on which the enzyme acts) and it is designed so that the enzyme only recognizes one specific substrate. Because of this, enzymes are very specific and this is called enzyme substrate specificity.

Let’s now discuss the Enzyme Substrate Complex. This complex deals with the ability of an enzyme and its substrate to combine and produce a product. I would like you to think of a key and a lock. Only one specific key can fit into its respective lock. In this analogy, the key represents the enzyme and the lock represents the substrate. They are designed for each other exclusively. If the substrate doesn’t fit the enzyme perfectly, then no chemical reaction will take place.

The Roles of Coenzymes and Inorganic Cofactors

Coenzymes are organic compounds that transport molecules from one enzyme to another. They belong to the bigger group of cofactors (which we will go over shortly) and are required by some enzymes to accomplish catalysis. Though they are not considered substrates of the reaction, they do bind to the enzyme’s active site loosely in order to help them complete their activities. Coenzymes don’t become an essential part of the reaction. The covalent bond between enzyme and coenzyme is broken instead and the coenzyme retreats back to its free floating state until it is needed again.

Inorganic cofactors are metal ions. In humans, the list generally includes iron, manganese, cobalt, copper, zinc, selenium and molybdenum. Cofactors are sometimes required to increase the rate of catalyst.

Enzyme Inhibitors and Regulators

As you might have guessed from the name, an enzyme inhibitor doesn’t react with the enzyme. The inhibitor has a comparable shape to the substrate for the enzyme and the inhibitor contends with the substrate for the active site. Though once it attaches to the active site, it doesn’t react. It pretty much just gets in the way. The complex doesn’t react to form products and as a result it splits up again to return to the form of enzyme and inhibitor molecule.

Regulatory mechanisms of enzymes involve not only inhibition but also activation. These controls are achieved by controlling a few enzymes in a series of reactions which happen in a sequence. The product of one complex becomes the substrate for the following step and so on. The entire set of actions can be managed by manipulating the initial enzyme of the series.

Continue to Energy Transformation study guide page

Share This Articles