What is the Difference Between ALT and AST

The key difference between ALT and AST is that ALT (alanine transaminase) is an enzyme that catalyzes the transfer of an amino group from L-alanine to α-ketoglutarate while AST (aspartate transaminase) is an enzyme that catalyzes the transfer of an amino group from L-aspartate to α-ketoglutarate.

Liver enzymes are proteins that normally speed up chemical reactions in the body. These chemical reactions include the production of bile, the production of substances that help blot clotting, breaking down food and toxins, and fighting against infections. Some common liver enzymes include ALP (alkaline phosphatase), ALT (alanine transaminase), AST (aspartate transaminase), and GGT (gamma-glutamyl transferase). If the liver is injured, these enzymes are released into the bloodstream.

CONTENTS

1. Overview and Key Difference
2. What is ALT
3. What is AST
4. Similarities – ALT and AST
5. ALT vs AST in Tabular Form
6. Summary – ALT vs AST

What is ALT (Alanine Transaminase)?

ALT is an enzyme that catalyzes the transfer of an amino group from L-alanine to α-ketoglutarate. The products of this reversible transamination reaction are pyruvate and glutamate. ALT is an enzyme that is found in the liver. It was formerly called serum glutamate-pyruvate transaminase or serum glutamic-pyruvic transaminase (SGPT). ALT was first characterized by Arthur Karmen and colleagues in 1950. ALT requires the coenzyme pyridoxal phosphate for its actions. In ALT catalyzed reactions, pyridoxal phosphate is converted into pyridoxamine in the first phase of the reaction, when an amino acid is converted into a ketoacid. ALT is most commonly found in the liver. It is also present in various body tissues and plasma.

Moreover, the half-life of ALT in circulation is around 47 hours. ALT is cleared by sinusoidal cells in the liver. Furthermore, elevated levels of ALT often suggest the presence of medical conditions such as viral hepatitis, diabetes, congestive heart failure, liver damage, bile duct problems, infectious mononucleosis, or myopathy.

What is AST (Aspartate Transaminase)?

AST is an enzyme that catalyzes the transfer of an amino group from L-aspartate to α-ketoglutarate. AST also catalyzes the interconversion of aspartate and α-ketoglutarate to oxaloacetate and glutamate. It is an enzyme that is found in the liver, brain, pancreas, heart, kidneys, lungs, and skeletal muscles. As a prototypical transaminase, the enzyme AST relies on PLP (pyridoxal phosphate) to transfer the amino group from aspartate to the corresponding keto acid. There are two isoenzymes found for this particular AST enzyme. The cytosolic enzyme (GOT1/cAST) derives mainly from red blood cells and the heart. The mitochondrial isoenzyme (GOT2/mAST) is present predominantly in the liver.

Moreover, this enzyme was first described by Arthur Karmen and colleagues in 1954. The half-life of total AST in circulation is around 17 hours (on average 87 hours for mitochondrial AST). This enzyme is also cleared by sinusoidal cells in the liver. Furthermore, elevated levels of AST may indicate diseases such as myocardial infarction, acute pancreatitis, acute hemolytic anemia, severe burns, acute renal disease, musculoskeletal diseases, and trauma.

What are the Similarities Between ALT and AST?

• ALT and AST are two liver enzymes.
• Both are transaminase enzymes.
• Both catalyze the transfer of an amino group from amino acid to corresponding keto acid.
• They need PLP (pyridoxal phosphate) for their reactions.
• Both were first described by Arthur Karmen.
• ALT/AST ratio is commonly measured clinically as a biomarker for liver health.
• They are usually cleared by sinusoidal cells in the liver.

What is the Difference Between ALT and AST?

ALT (alanine transaminase) is an enzyme that catalyzes the transfer of an amino group from L-alanine to α-ketoglutarate while AST (aspartate transaminase) is an enzyme that catalyzes the transfer of an amino group from L-aspartate to α-ketoglutarate. Thus, this is the key difference between ALT and AST. Furthermore, ALT is found predominantly in the liver, with negligible quantities found in the kidneys, heart, and skeletal muscle. On the other hand, AST is found in the liver, heart, skeletal muscle, kidneys, brain, and red blood cells.

The below infographic presents the differences between ALT and AST in tabular form for side by side comparison.

Summary – ALT vs AST

ALT and AST are two liver transaminase enzymes. ALT catalyzes the transfer of an amino group from L-alanine to α-ketoglutarate, while AST catalyzes the transfer of an amino group from L-aspartate to α-ketoglutarate. So, this is the summary of the difference between ALT and AST.