Clinical Chemistry 2: AST Isoenzymes

Questions and Answers

In which conditions are the highest levels of aspartate aminotransferase (AST) observed?

Cirrhosis (correct)

Acute myocardial infarction

Skeletal muscle injury

Viral hepatitis (correct)

What is the primary tissue source for high concentrations of AST?

Skeletal muscle

Kidney

Erythrocytes

Cardiac tissue (correct)

What would be a significant source of error in AST testing?

Using a freshly drawn serum sample

Conducting the assay with the appropriate controls

Delayed transport of the serum sample (correct)

Storing the serum at room temperature (correct)

Which of the following statements about serum stability of AST is true?

Serum should be refrigerated for optimal stability Signup and view all the answers

What is an expected AST level increase in cases of skeletal muscle involvement?

4-8 times ULN Signup and view all the answers

What is the primary role of aspartate aminotransferase (AST) in metabolic processes?

To facilitate the transfer of amino groups between aspartate and α-keto acids Signup and view all the answers

Which coenzyme is required for the enzymatic activity of aspartate aminotransferase?

Pyridoxal phosphate (Vitamin B6) Signup and view all the answers

What could be a common source of error in the testing of AST levels?

Delayed transport of serum samples Signup and view all the answers

Which is true regarding the isoenzymes of aspartate aminotransferase?

Different isoenzymes can indicate specific tissue damage Signup and view all the answers

What is the typical reference value range for serum AST levels in adults?

10 to 40 U/L Signup and view all the answers

In the clinical analysis of AST, which condition might be indicated by elevated AST levels?

Liver cirrhosis Signup and view all the answers

What is one critical factor in ensuring serum stability and storage for AST testing?

Keeping samples at 4°C until analysis Signup and view all the answers

Which method is commonly used to determine the enzymatic activity of AST?

Spectrophotometry Signup and view all the answers

Which isoenzyme of Aspartate Aminotransferase (AST) is predominantly found in serum?

Cytoplasmic Isoenzyme Signup and view all the answers

What is the significance of increased levels of the mitochondrial isoenzyme of AST?

It suggests cellular necrosis. Signup and view all the answers

What enzyme activity assessment method is the basis for measuring AST activity?

Karmen Method Signup and view all the answers

What is the optimal pH range for the enzyme activity assay of AST?

7.3 to 7.8 Signup and view all the answers

What reference range is established for AST activity at 37°C?

5 to 35 U/L Signup and view all the answers

Which substance is used as an indicator in the AST enzyme activity assay?

Malate Dehydrogenase Signup and view all the answers

What is one reason why isoenzyme analysis of AST is not routinely performed?

It is too time-consuming compared to other tests. Signup and view all the answers

What can cause errors in AST testing results?

Improper sample handling Signup and view all the answers

Study Notes

Isoenzymes of Aspartate Aminotransferase (AST)

Two isoenzymes: Cytoplasmic (predominant in serum) and Mitochondrial (increased in cellular necrosis).
Intracellular AST concentration is 7,000 times higher than extracellular levels.
Isoenzyme analysis is not routinely performed in clinical settings.

Assay for AST Enzyme Activity

Based on Karmen Method utilizing a coupled enzymatic reaction.
Monitored using Malate Dehydrogenase, tracking absorbance changes at 340 nm.
Measures the oxidation of NADH to NAD+.
Optimal pH range is between 7.3 to 7.8.
Reference range for AST activity is 5 to 35 U/L (37°C), equivalent to 0.1 to 0.6 µkat/L.

Nomenclature and Function of AST

Enzyme Classification: E.C. 2.6.1.1.
Formerly known as Serum Glutamic Oxaloacetic Transaminase (SGOT).
Catalyzes transfer of an amino group between aspartate and α-keto acids.
Coenzyme required for activity: Pyridoxal phosphate (Vitamin B6).

Tissue Sources of AST

High concentrations found in cardiac tissue, liver, and skeletal muscle.
Lower concentrations noted in kidneys, pancreas, and erythrocytes.

Diagnostic Significance of AST

Markedly elevated in acute hepatocellular disorders, with viral hepatitis levels reaching up to 100 times the upper limit of normal (ULN).
Cirrhosis levels are approximately 4 times ULN.
In skeletal muscle involvement, AST levels may increase 4-8 times ULN.
Can indicate acute myocardial infarction (AMI).

Clinical Relevance of Aminotransferases

Used to evaluate liver function and muscle damage.
Results correlate with both physiologic and pathologic conditions, aiding in diagnosis and management of diseases.

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Description

This quiz covers the study of Aspartate Aminotransferase (AST) isoenzymes, focusing on their characteristics and clinical significance. It includes details about cytoplasmic and mitochondrial isoenzymes, as well as their concentration differences. Test your knowledge on how these isoenzymes are analyzed in clinical settings.