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What is an Isozyme? - Definition & Electrophoresis

Instructor: Erika Steele

Erika has taught college Biology, Microbiology, and Environmental Science. She has a PhD in Science Education.

Sometimes enzymes come in multiple forms called isozymes. This lesson will discuss the characteristics of isozymes and describe how these variations can be isolated from cells and separated from each other.

What Is an Isozyme?

Enzymes are proteins that make things happen in cells. For example, enzymes produce energy, restore DNA mutations, move things across the plasma membrane and many other things that make life possible for cells. Think of all the things a cell has to do, enzyme regulation becomes complex quick!

However, things get even crazier when you start thinking about enzyme regulation in multicellular organisms. Multicellular organisms have many cells, organs, and different stages of life that require enzymes to function.

With this in mind, you would need a lot of enzymes. How would you resolve the problem of regulating enzymes? Perhaps make multiple enzymes with the same function? This is exactly what happens. In fact, there are two ways that our bodies can make variations of an enzyme.

  1. A single gene can make different variations of the enzyme called allozymes.
  2. Different genes can make different variations of the enzyme called isozymes.

Let's say that an enzyme is needed to make a Twinkie you eat into energy. We'll call it Twinkinase. A single gene could make a variant of Twinkinase, or multiple genes could code for different variants.

Figure 1: Twinkinase comes in multiple forms. Although Gene A produces several allozymes, while the other genes produce isozymes.
allozymes

Regardless of how the variations of enzymes are produced, the result is the same. You end up with multiple forms of an enzyme that have different amino acid sequences and therefore different shapes, sizes, and electrical charges, but the same function. From this point, this lesson will only discuss isozymes.

Why Use Isozymes?

It may seem like a huge effort to have so many genes for one enzyme when the enzyme could just be transported or made where it is needed. However, the main reason for isozymes is that enzymes have limited conditions such as temperature, salinity, and pH, at which they will work. Each gene that produces an isozyme with a unique amino acid sequence allows for a variety of isozymes that will work under a range of those conditions.

Let's use the isozymes of Twinkinase to illustrate this point.

  • Organs in the body may have a variety of isozymes because these organs serve diverse functions and have dissimilar internal conditions. An isozyme of Twinkinase that would work in the stomach may not work in the muscles because the stomach and muscles vastly differ in pH.
  • The isozymes might be expressed at different stages in an organism's life cycle where the requirement for the energy that Twinkinase produces might vary.
  • Cancer cells grow abnormally quick and can travel around the body. They'll need extra energy, so they may express a different isozyme of Twinkinase that works at a faster rate than other Twinkinases.

Figure 2: Isozymes allow the function of an enzyme to work under various conditions, at different stages, or in a variety of cellular conditions such as cancer.
isozymes_conditions

How Can You Isolate Isozymes?

If you were interested in isolating a single isozyme of Twinkinase only expressed in the pinky toe, what do you think the first step would be? Well, first you would need a way to separate Twinkinase from other proteins and enzymes floating in the pinky toe. This is simple if you only have one form of Twinkinase. However, imagine this is not the case and there are multiple forms to deal with.

Gel electrophoresis is a lab method that separates molecules based on size and is one way in which you can isolate the isozyme you want from the pinky toe sample.

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