Podcast
Questions and Answers
Which LDH isoenzyme is predominantly found in the heart?
Which LDH isoenzyme is predominantly found in the heart?
- LDH-1 (correct)
- LDH-3
- LDH-4
- LDH-2
What is the adaptive significance of glucokinase, the glucose sensor in the pancreas?
What is the adaptive significance of glucokinase, the glucose sensor in the pancreas?
- Regulates blood glucose levels and prevents hyperglycemia after meals. (correct)
- Ensures survival by maintaining energy production under low glucose conditions.
- Acts as a glucose sensor in the pancreas and regulates glycogen synthesis in the liver.
- Provides a constant supply of glucose-6-phosphate for energy production in essential tissues.
What is the clinical relevance of hexokinase deficiency?
What is the clinical relevance of hexokinase deficiency?
- Causes nonspherocytic hemolytic anemia due to insufficient energy in red blood cells. (correct)
- Ensures survival by maintaining energy production under low glucose conditions.
- Associated with MODY (Maturity-Onset Diabetes of the Young), affecting blood glucose regulation.
- Provides a constant supply of glucose-6-phosphate for energy production in essential tissues.
Which LDH isoenzyme is mostly present in skeletal muscles?
Which LDH isoenzyme is mostly present in skeletal muscles?
How many subunits does the lactate dehydrogenase (LDH) enzyme have?
How many subunits does the lactate dehydrogenase (LDH) enzyme have?
Which enzyme type has the highest affinity for pyruvate?
Which enzyme type has the highest affinity for pyruvate?
What is the primary physiological role of LDH-5?
What is the primary physiological role of LDH-5?
Which LDH isozyme is primarily expressed in the lungs?
Which LDH isozyme is primarily expressed in the lungs?
What type of subunits compose LDH-2?
What type of subunits compose LDH-2?
Which LDH isozyme is best suited for anaerobic conditions?
Which LDH isozyme is best suited for anaerobic conditions?
Which LDH enzyme has a moderate affinity for pyruvate?
Which LDH enzyme has a moderate affinity for pyruvate?
What type of conditions does LDH-1 operate best under?
What type of conditions does LDH-1 operate best under?
Which organ is primarily associated with the expression of LDH-5?
Which organ is primarily associated with the expression of LDH-5?
What defines isoenzymes?
What defines isoenzymes?
Which characteristic do isoenzymes NOT differ in?
Which characteristic do isoenzymes NOT differ in?
How do hexokinase and glucokinase differ in terms of affinity for glucose?
How do hexokinase and glucokinase differ in terms of affinity for glucose?
What is a key feature of isoenzymes regarding tissue specificity?
What is a key feature of isoenzymes regarding tissue specificity?
What distinguishes the regulatory mechanisms of isoenzymes?
What distinguishes the regulatory mechanisms of isoenzymes?
Which function is associated with hexokinase?
Which function is associated with hexokinase?
In which condition is glucokinase primarily active?
In which condition is glucokinase primarily active?
Which of the following best describes the Km value of hexokinase?
Which of the following best describes the Km value of hexokinase?
What does a flipped LDH profile generally indicate?
What does a flipped LDH profile generally indicate?
In healthy individuals, which LDH isoenzyme is most abundant?
In healthy individuals, which LDH isoenzyme is most abundant?
How does LDH-1 change after a myocardial infarction?
How does LDH-1 change after a myocardial infarction?
Which enzyme plays a crucial role in energy metabolism in muscle and cardiac tissues?
Which enzyme plays a crucial role in energy metabolism in muscle and cardiac tissues?
What condition is NOT typically associated with a flipped LDH profile?
What condition is NOT typically associated with a flipped LDH profile?
What does creatine kinase catalyze the conversion of?
What does creatine kinase catalyze the conversion of?
Which LDH isoenzyme is primarily found in the heart?
Which LDH isoenzyme is primarily found in the heart?
What is a primary function of creatine kinase in cardiac muscle?
What is a primary function of creatine kinase in cardiac muscle?
Flashcards
Isoenzymes
Isoenzymes
Structurally distinct forms of the same enzyme, catalyzing the same reaction.
Amino Acid Sequence
Amino Acid Sequence
The order of amino acids in a protein, defining its structure.
Tissue Specificity
Tissue Specificity
Different isoenzymes are expressed in specific tissues for metabolic regulation.
Kinetic Properties
Kinetic Properties
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Hexokinase
Hexokinase
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Glucokinase
Glucokinase
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Affinity for Glucose (Km)
Affinity for Glucose (Km)
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Regulation of Isoenzymes
Regulation of Isoenzymes
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LDH-1
LDH-1
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LDH-5
LDH-5
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Optimal Conditions LDH-1
Optimal Conditions LDH-1
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Physiologic Role LDH-4
Physiologic Role LDH-4
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Kinetic Properties LDH-5
Kinetic Properties LDH-5
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LDH-2
LDH-2
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Physiologic Role LDH-1
Physiologic Role LDH-1
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Optimal Conditions LDH-5
Optimal Conditions LDH-5
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Glucokinase Function
Glucokinase Function
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Hexokinase Deficiency
Hexokinase Deficiency
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LDH Structure
LDH Structure
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Isoenzyme Types
Isoenzyme Types
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MODY
MODY
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Flipped LDH Profile
Flipped LDH Profile
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Normal LDH Profile
Normal LDH Profile
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Acute Myocardial Infarction
Acute Myocardial Infarction
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Creatine Kinase (CK)
Creatine Kinase (CK)
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Creatine Phosphate
Creatine Phosphate
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Isoenzymes of CK
Isoenzymes of CK
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Study Notes
Isoenzymes
- Isoenzymes (or isozymes) are different forms of the same enzyme, structurally distinct but catalyzing the same chemical reaction.
- They differ in amino acid sequence and physicochemical properties (e.g., pH stability, electrophoretic mobility).
- Key features include:
- Tissue specificity: Different isoenzymes are expressed in different tissues, enabling tailored metabolic regulation.
- Kinetic properties: Isoenzymes vary in substrate affinity (Km) and reaction velocity (Vmax).
- Regulatory mechanisms: Isoenzymes differ in sensitivity to allosteric effectors or inhibitors.
Examples of Isoenzymes and Their Significance
-
Hexokinase and Glucokinase:
- Hexokinase: Ubiquitous, low Km, high affinity, inhibited by product (glucose-6-phosphate), active at low glucose.
- Glucokinase: Primarily in liver and pancreatic beta cells, high Km, low affinity, active at higher glucose concentrations, not inhibited by glucose-6-phosphate.
- Function in glucose regulation.
-
Lactate Dehydrogenase (LDH):
- Tetrameric enzyme with (muscle) M and (heart) H subunits.
- Different LDH isoenzymes (e.g., LDH-1, LDH-2, LDH-3, LDH-4, LDH-5) are formed by various combinations of these subunits.
- Isozyme profiles can be diagnostic, indicating tissue damage (e.g., myocardial infarction, hemolysis).
- Flipped LDH profile: a possible clue for a heart attack or other conditions affecting tissue degradation.
-
Creatine Kinase (CK):
- Catalyzes the reversible conversion of creatine phosphate and ADP to creatine and ATP, supporting energy production in muscles, brain, and heart.
- Three isoenzymes: CK-MM (muscle), CK-MB (cardiac), and CK-BB (brain).
- CK-MB is a specific marker for myocardial infarction.
-
Alkaline Phosphatase (ALP):
- Involved in dephosphorylation, active in alkaline environments.
- Different tissue-specific isoenzymes (bone-specific, liver, intestinal, placental, germ cell) allowing for differential diagnosis.
- Elevated levels might indicate bone diseases or liver disorders.
Detection Methods
- Electrophoresis separates isoenzymes based on charge and size.
- Immunoassays utilize specific antibodies to detect and quantify isoenzymes.
- Spectrophotometry measures enzyme activity through detecting absorbance changes.
- Chromatography separates isoenzymes based on their physicochemical properties.
- Heat inactivation tests differentiate isoenzymes based on their thermal stability.
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