Difference Between Protein Kinase A and Protein Kinase C

The key difference between protein kinase A and protein kinase C is that protein kinase A is a type of protein kinase that is dependent on cyclic AMP, while protein kinase C is a subfamily of protein kinases that is responsive to lipid signalling.

Kinase is an enzyme that catalyzes the transfer of phosphate group from high-energy, phosphate-donating molecules to specific substrates. We call this process phosphorylation. Kinases regulate the majority of cellular pathways, including signal transduction. Protein kinases are a specific type of kinases that catalyze protein phosphorylation or transfer phosphate to precise substrate proteins. These enzymes regulate the biological activity of proteins by phosphorylation of specific amino acids with phosphate groups from ATP. Once phosphorylation occurs, inactive proteins transform into active proteins due to the conformational change. Protein kinase C and protein kinase A are two types of protein kinase families that belong to the subfamily: AGC kinase of protein kinases.

CONTENTS

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

What is Protein Kinase A?

Protein kinase A is a type of protein kinase that is dependent on cyclic AMP. Hence, it is also known as cyclic AMP-dependent protein kinase or A kinase. Its main function is to phosphorylate proteins with phosphate groups. Since protein kinase A is dependent on cyclic AMP, its activity is regulated by the fluctuating levels of cyclic AMP within the cells. Moreover, protein kinase A acts as the end effector for a variety of hormones that work through a cyclic AMP signalling pathway. Hence, this enzyme is responsible for all cellular responses.

Structurally, protein kinase A is a heterotetramer composed of two subunits: catalytic subunit and a regulatory subunit. The activity of protein kinase A can also be reduced or inhibited by protein kinase inhibitors. These inhibitors often act as pseudosubstrates for the catalytic subunit.

What is Protein Kinase C?

Protein kinase C is a subfamily of protein kinases and is responsive to lipid signalling. The subfamily consists of fifteen isozymes in humans. Isozymes differ from the second messenger requirements. Protein kinase C consists of two domains: the regulatory domain and catalytic domain. In fact, protein kinase C is a multifunctional protein serine kinase which participates in a wide variety of neuronal functions.

Moreover, Protein kinase C acts as a central component of many crucial cell signalling cascades. Besides, protein kinase C is responsible for regulating transcription, mediating immune responses, regulating cell growth and modulating membrane structure.

What are the Similarities Between Protein Kinase A and Protein Kinase C?

• Both protein kinase A and protein kinase C are AGC kinases.
• Thus, they belong to a subfamily of protein kinases called AGC kinase.
• They play important roles in several signal transduction cascades in living organisms.
• Structurally, they consist of two subunits as a regulatory domain and a catalytic domain.
• Their activity can be inhibited by protein kinase inhibitors.

What is the Difference Between Protein Kinase A and Protein Kinase C?

Protein kinase A and protein kinase C are two subfamilies of protein kinases that belong to AGC kinases. Protein kinase A is a protein kinase that is dependent on cyclic AMP and acts as the end effector for a variety of hormones. Meanwhile, protein kinase C is a protein kinase that is responsive to lipid signalling. So, this is the key difference between protein kinase A and protein kinase C.

Summary – Protein Kinase A vs Protein Kinase C

Protein kinase is an enzyme that modifies other proteins by adding a phosphate group to them. Protein kinase A and protein kinase C are two subfamilies of AGC kinases of protein kinases. Protein kinase A is dependent on cyclic AMP. In contrast, protein kinase C is a specific type of kinase that mediates signal transduction cascade by hydrolyzing lipids. So, this is the key difference between protein kinase A and protein kinase C.

Reference:

1. “Protein Kinase C.” Protein Kinase C – an Overview | ScienceDirect Topics, Available here.
2. “Protein Kinase A.” Wikipedia, Wikimedia Foundation, 16 Nov. 2019, Available here.

Image Courtesy:

1. “PKARII” By Yikrazuul; chris 論 – File:Proteinkinase 1.svg, de:File:PKARII.png (Public Domain) via Commons Wikimedia
2. “Activation protein kinase C” By Yikrazuul – Own work; ISBN 978-3-8273-7312-0; ISBN 978-0781798754 (CC BY-SA 3.0) via Commons Wikimedia