Deactivation of Enzymes — Overview & Examples

When Does a Protein Become Denatured?

Enzymes are biological catalysts. So, like most catalysts, they work best under certain conditions.

If you think of making a soup, it won't really work unless you turn on the stove-top and heat it up. If you heat it too much, you'll burn the soup. Similarly, enzymes need certain conditions to work at their best. These conditions are kept through homeostasis.

The activity of enzymes is dependent on temperature, pH, and regulatory molecules. If the enzyme is placed in conditions that it doesn't like, it can become denatured. Denatured enzymes can be thought of as the burnt soup: just ruined.

$$\color{#8925AE}{\text{Vocabulary Review:}}$$

$\color{#8925AE}{\text{Enzyme}}$ : A protein that acts like a catalyst. It speeds up biological reactions but is not used up during the reaction

$\color{#8925AE}{\text{Activation Energy}}$ : Minimum amount of energy needed to begin a chemical reaction

$\color{#8925AE}{\text{Catalyst}}$ : A substance that speeds up reactions but is not used up during the reaction

$\color{#8925AE}{\text{Substrate}}$ : Molecules that a specific enzyme binds to and recognizes. They are transformed during the reaction

What Causes Enzymes to Deactivate?

Enzymes can be deactivated by a range of factors. Often, this happens because of changes in temperature or pH.

Enzymes are picky. Each enzyme has a small range of temperatures and pH levels at which it works best. We call this optimum pH and optimum temperature. If either one falls out of range, the enzyme works much less efficiently. Often, even small changes can result in complete deactivation of an enzyme.

I like to compare enzyme deactivation to my workout habits. It's usually something like this:

It's January and "new year, new me". I plan to start jogging every day, but it's too cold for that nonsense, so I push it off until the days get warmer. Now once spring comes around, the temperature is just right. I'm jogging every day and feeling good. We get to July. It is smoldering hot outside, and honestly I'm just worried about UV radiation and the possibility of a heat stroke. So I push off jogging again. It's really not my fault. It's the weather.

Likewise, enzymes will also only work when the conditions are just right.

What Happens to an Enzyme When the Temperature or pH Changes?

The further we stray from an enzyme's optimum conditions, the less active it is. The enzyme begins to denature. This means that its structure changes. As you probably know, the shape of an enzyme is critical to its function. In order to do its job, an enzyme has to be able to bind to its target substrate. When the shape of an enzyme (and more specifically its active site) changes, it is no longer able to bind to its substrate. The enzyme is deactivated and no longer has an effect on the rate of the reaction.

Enzymes can also be deactivated by other molecules. The reactions that take place within our bodies are under strict regulation. Some enzymes only work under certain conditions. Sometimes they only become active when a molecule binds to the active site or another region on the enzyme. Other times, the enzyme is always active unless a special molecule binds to it, either blocking the active site or changing its shape.

How Are Enzymes Deactivated?

There are a few ways to damage or destroy an enzyme. As we've hinted at, the shape of an enzyme is fundamental to its ability to work.

So, damaged enzymes are enzymes whose shapes have been altered in some way. Damaged enzymes no longer have a lock-and-key fit with their substrates, which means they can't catalyze the reaction.

Option 1: Denaturation

When an enzyme is denatured, it essentially melts and loses its shape. Denaturation can be caused by extreme heat and by changes in pH.

Option 2: Inhibition

While inhibitors don't necessarily destroy an enzyme, they do block it from working.

There are two types of inhibition to consider.

First, let's take a look at a normal enzyme-substrate reaction:

Now, let's look at the first type of inhibition: competitive inhibition.

In cases of competitive inhibition, an inhibitor molecule binds to the enzyme at its active site, blocking the substrate. The inhibitor and substrate compete for the active site (hence "competitive" inhibition).

Finally, let's look at the second type of inhibition: non-competitive inhibition.

In these cases, an inhibitor binds to an enzyme somewhere other than the active site, called the allosteric site. This binding, however, causes the active site to change shape, preventing the substrate from binding.

Key Vocabulary:

1. Enzyme
2. Substrate
3. Active site
4. Inhibitor
5. Denaturation

(Video) Enzymes, Feedback Inhibition, and Allosteric Regulation

by JKM12988

You probably know about what enzymes do when they're active. But are they ever not active, you ask? Yes, they are. The video above explains three ways that enzymes can be deactivated and why it happens.

The next video discusses changes in temperature and pH away from the enzyme's optimal conditions and how drastic changes can damage an enzyme molecule.

(Video) Denaturation of Enzymes

by FuseSchool - Global Education