Isoenzymes in Clinical Diagnosis

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Questions and Answers

What is the primary function of enzymes in living cells?

To consume substrates during chemical reactions

To increase the rate of chemical reactions (correct)

To synthesize new proteins

To reduce the temperature of cellular reactions

What is the characteristic of enzymes that distinguishes them from inorganic catalysts?

Inability to be denatured

Ability to increase reaction rate

High temperature stability

Specificity in their action (correct)

Which of the following is NOT a characteristic of enzymes?

They are consumed during chemical reactions (correct)

They are highly selective

They are thermolabile in character

They are protein in nature

What is the suffix commonly used in naming enzymes?

-ase Signup and view all the answers

What is the term for the substance upon which the enzyme acts to convert it to a product?

Substrate Signup and view all the answers

What is the category of enzymes that are produced inside cells and act outside the cells?

Extracellular enzymes Signup and view all the answers

What happens to enzymes when they are denatured?

They lose their biological function Signup and view all the answers

What is the rate of chemical reaction measured in terms of?

Change in amount of starting materials per unit time Signup and view all the answers

Which class of enzymes is primarily involved in oxidation-reduction reactions?

Oxidoreductases Signup and view all the answers

What is the role of coenzymes in enzyme activity?

They serve as non-protein components necessary for enzyme function. Signup and view all the answers

Which of the following enzymes is specifically termed as a conjugated protein?

Holoenzyme Signup and view all the answers

Which coenzyme is primarily a carrier of acyl groups?

Coenzyme A Signup and view all the answers

What type of reaction is catalyzed by hydrolases?

Cleavage of bonds by adding water Signup and view all the answers

Which of the following is a primary function of transferases?

To transfer functional groups other than hydrogen Signup and view all the answers

Which chemical structure is associated with the role of an apoenzyme?

The protein part of a conjugated enzyme Signup and view all the answers

What distinguishes lyases from other classes of enzymes?

They facilitate the addition or removal of chemical groups without hydrolysis. Signup and view all the answers

What is the primary mechanism of action of sulfanilamide?

It acts as a competitive inhibitor, competing with PABA for binding to the enzyme. Signup and view all the answers

Which of the following statements accurately describes non-competitive inhibition?

The inhibitor binds to a site other than the active site, affecting the enzyme's conformation and reducing its catalytic activity. Signup and view all the answers

How does the binding of heavy metal ions like Hg2+ affect enzyme activity?

Heavy metal ions act as non-competitive inhibitors, binding to a site other than the active site and altering the enzyme's conformation. Signup and view all the answers

Which of the following characteristics is NOT typically associated with irreversible inhibition?

The inhibitor binds to the enzyme-substrate complex, preventing product formation. Signup and view all the answers

Which of the following pairs correctly matches an irreversible inhibitor with its target enzyme?

Iodoacetate - Papain and Glyceraldehyde-3-phosphate dehydrogenase Signup and view all the answers

Which enzyme is specifically elevated in prostatic carcinoma detection?

Serum acid phosphatase Signup and view all the answers

What is the primary mode of action of penicillin antibiotics?

Interference with bacterial cell wall synthesis. Signup and view all the answers

What enzyme is primarily used as a marker for alcoholic liver diseases?

Serum-γ-glutamyl transpeptidase Signup and view all the answers

Which enzyme is significantly elevated in acute pancreatitis?

Lipase Signup and view all the answers

Which of the following statements is true about the effect of non-competitive inhibitors on enzyme kinetics?

Km value remains unchanged, while Vmax decreases. Signup and view all the answers

Which of the following is NOT a characteristic of competitive inhibition?

The inhibitor binds to the enzyme-substrate complex, preventing product formation. Signup and view all the answers

In muscle dystrophies, which of the following enzymes is NOT typically increased?

Lactate dehydrogenase Signup and view all the answers

Which enzyme is mainly associated with intrahepatic and extrahepatic cholestasis?

5'-Nucleotidase Signup and view all the answers

Which enzyme is a marker for neuroblastoma and lung cancer?

Neuron–specific enolase Signup and view all the answers

Which isoenzyme is the first to be released into circulation after a myocardial infarction?

Creatine phosphokinase (CPK) Signup and view all the answers

What is the time frame for the peak elevation of creatine phosphokinase (CPK) after myocardial infarction?

24-30 hours Signup and view all the answers

Which enzyme generally attains a peak value within 48 hours following a myocardial infarction?

Aspartate transaminase (AST) Signup and view all the answers

How long does it typically take for lactate dehydrogenase (LDH) to return to normal levels after a myocardial infarction?

10-15 days Signup and view all the answers

Which of the following enzymes is NOT primarily used to diagnose myocardial infarction?

Amylase (AMY) Signup and view all the answers

What distinguishes isoenzymes from one another?

Their immunological properties and Km values Signup and view all the answers

Which serum enzyme is the last to rise and also the last to return to normal levels following myocardial infarction?

Lactate dehydrogenase (LDH) Signup and view all the answers

What is the purpose of estimating multiple serum enzymes in clinical diagnosis?

To enhance the specificity of diagnosis Signup and view all the answers

Study Notes

Introduction to Enzymes

Enzymes act as biocatalysts, increasing reaction rates without changing themselves.
Primarily proteins, enzymes accelerate specific chemical reactions by lowering activation energy.
Found in all living cells, they convert substrates into products without being consumed.
Enzymes are globular proteins, highly selective, and can be denatured, losing functionality.

Enzyme Distribution

Enzymes categorized based on their site of action:
- Intracellular enzymes: Function within cells (e.g., metabolic enzymes).
- Extracellular enzymes: Produced in cells but act outside (e.g., digestive enzymes).

Nomenclature and Classification

Enzymes typically end in -ase derived from the substrate they act on (e.g., lipase for lipids).
Historical names like pepsin and trypsin provide limited functional insight.
Six major enzyme classes identified by the International Union of Biochemistry (IUB):
- Oxidoreductases: Catalyze oxidation-reduction reactions.
- Transferases: Transfer functional groups other than hydrogen.
- Hydrolases: Split bonds by adding water.
- Lyases: Add or remove groups without hydrolysis.
- Isomerases: Catalyze interconversion of isomers.
- Ligases: Link two molecules using energy from ATP.

Enzyme Structure and Activity

Enzymes can be simple proteins or conjugated proteins (holoenzymes).
Holoenzymes consist of the protein part (apoenzyme) and a non-protein cofactor.
Cofactors can be organic (coenzymes) or inorganic.

Important Coenzymes

Hydrogen carriers:
- NAD, NADP, FAD, FMN, lipoic acid, coenzyme-Q.
Group carriers (mostly derived from vitamins):
- Coenzyme A (acyl group), Thiamine pyrophosphate (TPP: CO2), Biotin (CO2), Pyridoxal phosphate (PLP: -NH2), Folic acid (one carbon), Cobalamine (methyl group).

Enzyme Inhibition

Competitive Inhibition: Sulfanilamide blocks enzyme using PABA to synthesize folic acid.
Non-competitive Inhibition:
- Inhibitor binds away from the active site, changing enzyme shape; Km remains unchanged, Vmax decreases.
- Heavy metals (Ag+, Pb2+, Hg2+) can act as non-competitive inhibitors.
Irreversible Inhibition: Inhibitors bind covalently, permanently inactivating enzymes (e.g., iodoacetate, DIFP).

Isoenzymes

Isoenzymes vary in structure and properties but catalyze the same reaction.
Examples include lactate dehydrogenase (LDH) and creatine kinase (CK).

Enzymes in Clinical Diagnosis

Multiple serum enzymes provide better disease diagnosis than a single enzyme measurement.

Enzymes in Myocardial Infarction (MI)

Key markers include:
- Creatine phosphokinase (CPK): First enzyme elevated within 6-18 hours, peaks in 24-30 hours.
- Aspartate transaminase (AST): Peaks within 48 hours, normalization takes 4-5 days.
- Lactate dehydrogenase (LDH): Peaks around 3-4 days, normalizes after 10-15 days.

Enzymes in Liver Diseases

Elevated serum enzymes diagnose liver dysfunction:
- Alanine transaminase (ALT), Aspartate transaminase (AST), Lactate dehydrogenase (LDH).
Specific markers for cholestasis: Alkaline phosphatase, 5’-Nucleotidase.
Serum γ-glutamyl transpeptidase indicates alcoholic liver disease.

Enzymes in Muscle Diseases

Elevated muscle enzymes in muscular dystrophies include:
- Creatine phosphokinase, Aldolase, Aspartate transaminase.

Enzymes in Cancers

Acid phosphatase: Marker for prostatic carcinoma.
Neuron-specific enolase: Marker for lung cancer, neuroblastoma.

Enzymes in Bone and Pancreatic Diseases

Alkaline phosphatase (ALP): Increased in rickets disease.
Amylase and Lipase: Significantly elevated in acute pancreatitis.

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Description

Understanding the physical and chemical properties of isoenzymes, including lactate dehydrogenase and creatine kinase, for accurate disease diagnosis.