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?

It is necessary for the preparatory phase of glycolysis. Signup and view all the answers

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

10% Signup and view all the answers

What is the Warburg effect in cancer cells?

Enhanced glycolysis and ATP production even in the presence of oxygen. Signup and view all the answers

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

Transported to the liver and kidney for oxidation. Signup and view all the answers

What is a major function of LDH in erythrocytes?

Converts pyruvate to lactate. Signup and view all the answers

What indicates a myocardial infarction when measuring LDH levels?

LDH-1 found to be greater than LDH-2 Signup and view all the answers

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

Phosphofructokinase Signup and view all the answers

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

Approximately ten days Signup and view all the answers

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

Decreases their transcription and synthesis Signup and view all the answers

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

Greater than 50 times increase in LDH-1 and LDH-2 Signup and view all the answers

What is the primary role of pyruvate dehydrogenase in metabolism?

To irreversibly convert pyruvate into acetyl CoA Signup and view all the answers

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

Pulmonary embolism Signup and view all the answers

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

Initiates an increase in glucokinase levels Signup and view all the answers

What is the primary role of LDH in anaerobic glycolysis?

To interconvert pyruvate and lactate while regenerating NAD+. Signup and view all the answers

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

Increased availability of substrates like ADP and Pi. Signup and view all the answers

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

It shifts the equilibrium towards lactate production. Signup and view all the answers

What occurs during pyruvate conversion to lactate facilitated by LDH?

NAD+ is regenerated from NADH. Signup and view all the answers

Which regulation type primarily modulates LDH activity during metabolic transitions?

Allosteric modulation. Signup and view all the answers

What is a consequence of ethanol consumption on LDH activity?

Enhanced conversion of pyruvate to lactate. Signup and view all the answers

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

Hydride ion. Signup and view all the answers

What can LDH assays help identify in the body?

Tissue damage by measuring LDH levels. Signup and view all the answers

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.