Holoenzyme: Definition & Overview

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: Substrate Concentration: Definition & Effect on Enzyme Activity

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
Your next lesson will play in 10 seconds
  • 0:00 Enzyme Review
  • 1:13 What Is a Holoenzyme?
  • 2:04 Function of a Holoenzyme
  • 3:59 Lesson Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Speed Speed Audio mode

Recommended Lessons and Courses for You

Lesson Transcript
Instructor: Darla Reed

Darla has taught undergraduate Enzyme Kinetics and has a doctorate in Basic Medical Science

This lesson provides a quick review of the definition and function of an enzyme. It then defines a holoenzyme, explains its functions, and gives a few examples.

Enzyme Review

Your best friend has bought you a present, but he lives far, far away. What's the fastest way for him to get the present to you? He could walk, but that would take a long time. Riding a bike, driving, or even taking a plane would be much faster.

Without enzymes, chemical reactions in a cell occur at a similar speed to your friend walking to bring you that present. Enzymes are proteins that - like the bike, car, or plane that can help your friend get to you faster - speed up (or catalyze) cellular chemical reactions. They bind substrates and turn them into products.

In our analogy, the substrate would be the present from your friend, while the final product would be the delivered gift. So, the enzymes (bikes, cars, or planes) catalyze the change in substrate (wrapped present) to product (usable gift).

There is a special place on enzymes, called the active site, where substrates bind and are changed into products. But, the active site is not the only place where molecules can bind to enzymes. Molecules can also bind to other areas on enzymes to regulate (or control) enzyme activity. Non-substrates that bind enzymes and help catalyze reactions are called cofactors.

What Is a Holoenzyme?

A plane can take off with just a pilot, but he or she needs the assistance of a co-pilot for various tasks, including pre-flight checks to ensure everything is a go. Likewise, many enzymes need the help of cofactors to function. Cofactors can be inorganic ions (like metal zinc) or non-protein, organic (carbon-containing) molecules, known as coenzymes. Just as co-pilots can help fly many different planes, the same cofactor can bind to many different enzymes.

What do cofactors have to do with holoenzymes? An enzyme that needs a cofactor but does not have one is referred to as an apoenzyme. An apoenzyme with a cofactor attached is a holoenzyme. Holoenzymes, then, are enzymes with a bound cofactor, like a plane with its strapped-in co-pilot, ready for take-off.

Function of a Holoenzyme

An apoenzyme is inactive; that is, it will not catalyze substrates into products. An apoenzyme needs to become a holoenzyme (apoenzyme + cofactor) in order to function. The function of a holoenzyme is to change substrate into product, just like an enzyme does, but holoenzymes require a cofactor to be present. Additionally, holoenzymes are often made up of smaller protein parts called subunits.

To unlock this lesson you must be a Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account