Lactate Dehydrogenase Overview
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Questions and Answers

What happens to lactate produced during anaerobic metabolism in muscles?

  • It is transported to the liver for conversion to pyruvate. (correct)
  • It is metabolized immediately in the muscles.
  • It can be used directly for ATP production in tissues.
  • It is stored in muscle cells until oxygen is available.

    • What is the primary consequence of LDH activity in cancer cells compared to normal cells?

  • Enhanced aerobic metabolism through glycolysis. (correct)
  • Inability to convert pyruvate to lactate.
  • Decreased ATP production.
  • Increased formation of oxidative stress.

    • How many ATP molecules are generated from anaerobic glycolysis per glucose molecule?

  • 8 ATP
  • 2 ATP (correct)
  • 36 ATP
  • 4 ATP

    • What role does NAD+ play during anaerobic glycolysis?

    <p>It is necessary for the preparatory phase of glycolysis. (B)</p> Signup and view all the answers

    During resting conditions, what percentage of cerebral energy needs is met by lactate oxidation?

    <p>10% (C)</p> Signup and view all the answers

    What is the Warburg effect in cancer cells?

    <p>Enhanced glycolysis and ATP production even in the presence of oxygen. (D)</p> Signup and view all the answers

    In which form is lactate primarily utilized after being released by skeletal muscles?

    <p>Transported to the liver and kidney for oxidation. (B)</p> Signup and view all the answers

    What is a major function of LDH in erythrocytes?

    <p>Converts pyruvate to lactate. (C)</p> Signup and view all the answers

    What indicates a myocardial infarction when measuring LDH levels?

    <p>LDH-1 found to be greater than LDH-2 (D)</p> Signup and view all the answers

    Which enzyme's increase is primarily associated with the well-fed state due to carbohydrate consumption?

    <p>Phosphofructokinase (A)</p> Signup and view all the answers

    How long does the increase in LDH persist following an acute myocardial infarction?

    <p>Approximately ten days (C)</p> Signup and view all the answers

    What effect does high glucagon and low insulin have on glycolytic enzymes?

    <p>Decreases their transcription and synthesis (C)</p> Signup and view all the answers

    Which LDH isoenzymes indicate megaloblastic anemia when their levels exceed a certain threshold?

    <p>Greater than 50 times increase in LDH-1 and LDH-2 (C)</p> Signup and view all the answers

    What is the primary role of pyruvate dehydrogenase in metabolism?

    <p>To irreversibly convert pyruvate into acetyl CoA (D)</p> Signup and view all the answers

    What condition is indicated by an increase in LDH-3 levels?

    <p>Pulmonary embolism (D)</p> Signup and view all the answers

    What is the effect of regular meals rich in carbohydrates on glucokinase levels?

    <p>Initiates an increase in glucokinase levels (C)</p> Signup and view all the answers

    What is the primary role of LDH in anaerobic glycolysis?

    <p>To interconvert pyruvate and lactate while regenerating NAD+. (D)</p> Signup and view all the answers

    Which factor influences the activity of LDH during extreme muscular activity?

    <p>Increased availability of substrates like ADP and Pi. (A)</p> Signup and view all the answers

    How does a high NADH/NAD+ ratio affect the LDH equilibrium?

    <p>It shifts the equilibrium towards lactate production. (C)</p> Signup and view all the answers

    What occurs during pyruvate conversion to lactate facilitated by LDH?

    <p>NAD+ is regenerated from NADH. (A)</p> Signup and view all the answers

    Which regulation type primarily modulates LDH activity during metabolic transitions?

    <p>Allosteric modulation. (A)</p> Signup and view all the answers

    What is a consequence of ethanol consumption on LDH activity?

    <p>Enhanced conversion of pyruvate to lactate. (A)</p> Signup and view all the answers

    In LDH's catalytic mechanism, what ion is transferred from NADH to pyruvate?

    <p>Hydride ion. (A)</p> Signup and view all the answers

    What can LDH assays help identify in the body?

    <p>Tissue damage by measuring LDH levels. (C)</p> Signup and view all the answers

    Flashcards

    Lactate Dehydrogenase (LDH)

    An enzyme that converts lactate to pyruvate and vice-versa.

    Cori Cycle

    Metabolic pathway where lactate produced in muscles is converted to glucose in the liver.

    Anaerobic Glycolysis

    Glucose breakdown without oxygen, resulting in lactate production.

    Warburg Effect

    Cancer cells preferentially use glycolysis even with oxygen.

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    LDH Subunit Variation

    Different LDH compositions in different tissues due to specific metabolic needs.

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    Hyperlactatemia

    High levels of lactate in the blood.

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    Lactate Utilization

    Lactate is mostly used by liver and kidneys for glucose production.

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    Aerobic Metabolism

    Energy production with oxygen availability.

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    LDH mechanism

    LDH catalyzes the conversion of pyruvate to lactate, using NADH as a hydride ion donor, speeding up the reaction.

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    LDH active site binding

    NADH binds to LDH first, which then facilitates binding of lactate.

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    LDH reaction steps

    Pyruvate, with bound NADH, converts to lactate. NAD+ and then pyruvate are released.

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    Rate-limiting step in LDH

    The dissociation of NADH and NAD+ from LDH is slowest.

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    LDH regulation by metabolism

    LDH activity is affected by switching to anaerobic respiration by changes in availability of substrates, allosteric effects, and/or transcriptional mechanisms.

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    LDH and substrate availability

    Increased substrate concentrations like those during intense exercise boost LDH activity.

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    LDH and NADH/NAD+ ratio

    High NADH/NAD+ ratio (e.g., in alcohol consumption) shifts the equilibrium towards lactate formation.

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    LDH assay

    LDH assays measure LDH in blood serum; helpful for diagnosing tissue damage.

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    LDH and Muscle Training

    LDH (Lactate Dehydrogenase) levels in blood increase in skeletal and cardiac muscles after 3-5 hours of intense exercise.

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    LDH-1/LDH-2 Ratio and MI

    High LDH-1 relative to LDH-2 (ratio>1) suggests myocardial infarction (heart attack).

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    LDH Levels and Myocardial Infarction

    A significant increase in serum LDH levels (often >50 times normal) is indicative of acute myocardial infarction (heart attack).

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    LDH and Muscular Dystrophy

    Elevated serum LDH-5 levels is a potential marker for muscular dystrophy.

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    LDH and Toxic Hepatitis

    A ten times or more increase in serum LDH levels indicates possible toxic hepatitis (liver inflammation).

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    LDH and Pulmonary Embolism

    High LDH-3 levels might suggest massive platelet destruction, a possible sign of pulmonary embolism (blood clot in lung).

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    LDH and Fluid Effusions

    Serum LDH compared to fluid LDH helps differentiate between exudate and transudate fluid build-ups (in the body cavities).

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    LDH and Testicular Cancer

    LDH is used to classify the stage of non-seminomatous testicular cancer.

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    Study Notes

    Lactate Dehydrogenase (LDH)

    • LDH is an important enzyme in anaerobic metabolism
    • It belongs to the oxidoreductase class, EC 1.1.1.27
    • Catalyzes the reversible conversion of lactate to pyruvate, reducing NAD+ to NADH
    • Found in all tissues, a key checkpoint in gluconeogenesis and DNA metabolism
    • Increased LDH may indicate liver disease, anemia, heart attack, bone fractures, muscle trauma, cancers, infections (encephalitis, meningitis, encephalitis, HIV)

    LDH as a Diagnostic Marker

    • LDH can be a non-specific marker for tissue turnover
    • Elevated levels or specific isozyme increases can suggest cancer but are not diagnostic of type
    • Needs additional tests (e.g., CK for muscle; ALT for liver; troponin for heart)
    • Hemolysis of blood sample can increase LDH levels artificially; red blood cells contain LDH
    • Cellular necrosis also increases LDH serum concentration
    • LDH is a cytoplasmic enzyme found in all tissues but high concentrations in muscle, liver, and kidney; red blood cells also contain moderate amounts

    LDH Isozymes

    • LDH exhibits five isomeric forms (LDH-1 to LDH-5) based on the number of muscle (M) and heart (H) subunits
    • Each isozyme has varying expression in different tissues.
    • LDH-1 is primarily in the heart, LDH-2 in reticuloendothelial systems (RBCs), LDH-3 in lungs, LDH-4 in kidneys, and LDH-5 in liver and skeletal muscle
    • The subunit composition influences substrate affinity, inhibition, isoelectric point, and electrophoretic mobility

    LDH at a Molecular Level

    • Four genes (LDHA, LDHB, LDHC, LDHD) encode for LDH
    • LDHA, LDHB, and LDHC produce L-forms (major form in vertebrates)
    • LDHD produces D-isomer of LDH
    • LDH-1 to LDH-5 are translational products of LDHA and LDHB genes
    • Four subunits (combinations of A and B) form the five different LDH forms

    LDH Function in Different Conditions

    • In anaerobic conditions (e.g., exercise, hypoxic conditions) cells utilize LDH to produce lactate from pyruvate
    • LDH catalyzes the reversible conversion of pyruvate to lactate using NADH
    • LDH is necessary for lactate conversion back to pyruvate in the liver (Cori cycle)

    LDH Function in Cancer

    • Cancer cells often have increased glycolysis (Warburg effect) and LDH activity to compensate for low oxygen conditions
    • LDH-5, especially, is associated with certain cancers and may be a marker for radio-sensitization

    Clinical Significance of LDH

    • LDH assays measure the amount of LDH in serum, which leaks from damaged tissues
    • Measuring the change in optical density at 340 nm due to NADH production is how reaction rate is estimated
    • LDH levels are typically 140-280 U/L, but values vary with conditions and age
    • Elevated or specific isozyme elevations can suggest various diseases (e.g., liver disease, kidney disease, muscle damage, heart attack, etc.), as well as cancer, inflammations, and other diseases
    • LDH is used for cancer staging, evaluating metastatic cancer, and assessing muscle response to training

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    Description

    This quiz explores the function and significance of Lactate Dehydrogenase (LDH) in anaerobic metabolism and its role as a diagnostic marker for various diseases. It covers its biochemical properties, enzyme classification, and the implications of elevated LDH levels in clinical contexts. Test your knowledge on this critical enzyme and its relevance in health and disease.

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