Difference Between Hexokinase and Glucokinase

The key difference between Hexokinase and Glucokinase is that the Hexokinase is present in all tissues other than liver and beta cells of the pancreas while the Glucokinase is present only in the liver and beta cells of the pancreas.

Hexokinase and Glucokinase are two isozymes that catalyze the same reaction at two different places. They convert glucose into glucose 6-phosphate, which is the first reaction of glycolysis. Therefore, by utilizing ATP, they add a phosphate group to glucose and modify the structure. However, these two enzymes share similarities as well as differences, which we will be discussing here.

CONTENTS

1. Overview and Key Difference
2. What is Hexokinase
3. What is Glucokinase
4. Similarities Between Hexokinase and Glucokinase
5. Side by Side Comparison – Hexokinase vs Glucokinase in Tabular Form
6. Summary

What is Hexokinase?

Hexokinase is the enzyme that catalyzes the conversion of glucose into glucose 6-phosphate in the majority of the tissues. Therefore, this enzyme is highly abundant in all tissue types other than liver and beta cells of the pancreas. It uses hexoses such as glucose, fructose, galactose, etc. as its substrate and adds a phosphate group and modifies the structure. For this conversion, it utilizes ATP (energy). It has a higher affinity towards the substrate and has a low Km and low Vmax value.

The product concentration inhibits hexokinase. Furthermore, it doesn’t get affected by the hormones. Even at the low concentration of glucose, hexokinase can act on them.

What is Glucokinase?

Glucokinase is an isozyme of hexokinase, which is a specific enzyme present in the liver and beta cells of the pancreas. Therefore, it works under a high concentration of glucose. Moreover, its Km and Vmax are high, and therefore, it has a low affinity towards glucose.

Glucokinase is also catalyzed by the first step of glycolysis, which converts glucose into glucose 6-phosphate. Similar to hexokinase, glucokinase also uses ATP for this conversion. The hormone insulin controls the activity of glucokinase. However, unlike hexokinase, glucokinase cannot be controlled by feedback inhibition.

What are the Similarities Between Hexokinase and Glucokinase?

• Both Hexokinase and Glucokinase use ATP during the catalysis.
• They induce structural changes.
• Both react with glucose.
• Both are isozymes
• They convert glucose into glucose 6-phosphate.

What is the Difference Between Hexokinase and Glucokinase?

Hexokinase and glucokinase are isozymes that catalyze the same reaction. However, hexokinase is abundant in all tissue types other than liver and beta cells of the pancreas while glucokinase is present in liver and beta cells of the pancreas. This is the key difference between hexokinase and glucokinase. Moreover, hexokinase has low Km and Vmax values compared to glucokinase. However, its affinity towards glucose is high in contrast to glucokinase. Also, hexokinase works at an even low concentration of glucose. But glucokinase works only at a high concentration of glucose. The below infographic presents more details on the difference between hexokinase and glucokinase.

Summary – Hexokinase vs Glucokinase

Both hexokinase and glucokinase catalyze the same reaction of glycolysis. Hexokinase is present in almost all tissues while glucokinase is present in the liver and beta cells of the pancreas. They use ATP to convert glucose into glucose 6-phosphate. The Km and Vmax values are low in hexokinase while they are high in glucokinase. Glucokinase works at higher concentration of glucose. On the other hand, hexokinase can work even at a low concentration of glucose. This is the difference between hexokinase and glucokinase.

Reference:

1.“Glucokinase.” Egyptian Journal of Medical Human Genetics, Elsevier. Available here  

Image Courtesy:

1.’Hexokinase-glucose’By Jmun7616 – Own work, (Public Domain) via Commons Wikimedia  
2.’Glucokinase’By Jmun7616 – Own work, (Public Domain) via Commons Wikimedia