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Questions and Answers
Why have CK-MB activity tests been increasingly replaced by CK-MB mass assays?
What does a CK-MB mass to CK-MB activity ratio of ≥3 indicate?
Which statement is true regarding troponins?
At what point does Troponin T (TnT) typically peak after a myocardial infarction?
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What is the primary function of lactate dehydrogenase (LDH)?
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What is the primary role of enzymes in living organisms?
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Which characteristic is NOT true for enzymes?
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What defines coenzymes in relation to enzymes?
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Which of the following is a type of reversible enzyme inhibitor?
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Which of these metals can be considered a cofactor?
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What is the effect of extreme heat on enzyme activity?
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Which statement about isoenzymes is correct?
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What type of substances can serve as enzyme inhibitors?
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Which isoenzyme of LDH is the fastest and heat stable?
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Which LDH isoenzyme is primarily found in the liver?
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What is the normal range of LDH in serum?
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In a myocardial infarction, which LDH isoenzyme significantly increases?
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What is the primary tissue type where myoglobin is found in high concentration?
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What is the duration of raised myoglobin levels after a muscle injury?
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Which peptide is secreted by the ventricles of the heart in response to excessive stretching of heart muscle cells?
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Which LDH isoenzyme has the slowest mobility and is heat liable?
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What does a low dibucaine number indicate in relation to cholinesterase variants?
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Which type of amylase is primarily found in mammals and works best at a neutral pH?
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What is the normal serum value range for amylase?
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How much does amylase concentration increase during acute pancreatitis?
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What should affected individuals with cholinesterase variants carry to inform healthcare providers?
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What is the role of BNP in the context of congestive heart failure?
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What condition is associated with high levels of hs-CRP?
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What is the consequence of cholinesterase deficiency?
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Which factor can cause decreased plasma cholinesterase activity?
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Which condition results in increased plasma cholinesterase activity?
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What distinguishes true cholinesterase from pseudo cholinesterase?
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What does pro-BNP indicate in the context of cardiac health?
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What is the effect of organophosphorus insecticides on cholinesterase?
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Study Notes
Enzymes
- Enzymes are biological catalysts that accelerate chemical reactions in living organisms without being altered themselves
- Enzymes convert substrates into products.
- They are proteins containing 16% nitrogen.
- They are precipitated by ammonium sulfate or trichloroacetic acid.
- Enzymes are water-soluble.
- They are sensitive to heat, with an optimal temperature of 10°C.
- Optimal pH for enzyme activity is 6-8
- Iso-enzymes are different physical forms of the same enzyme with the same activity.
Cofactors and Coenzymes
- Some enzymes require non-protein components for optimal activity. These are called cofactors and coenzymes.
- Cofactors are metal ions (e.g., Mg2+, Fe, Zn, etc.) that assist enzymes in facilitating chemical reactions.
- Coenzymes are organic molecules derived from vitamins (e.g., NAD, TPP, FAD, FMN, pantothenic acids, etc.) that act as transient carriers of specific functional groups for enzymes.
Enzyme Inhibitors
- Chemicals that bind to enzymes and alter their activity are called enzyme inhibitors.
- Inhibitors include drugs, antibiotics, toxins, and natural products.
- There are two general classes of inhibitors:
- Reversible Inhibitors: Bind reversibly to enzymes.
- Irreversible Inhibitors: Bind irreversibly to enzymes.
Creatine Kinase (CK) and Troponins
-
Creatine Kinase (CK):
- CK-MB activity tests are increasingly replaced by CK-MB mass assays.
- CK-MB mass measures the protein concentration of CK-MB, which rises earlier than CK-MB activity.
- A CK-MB mass/CK-MB activity ratio ≥ 3 is indicative of AMI, rather than muscle damage.
- CK levels are significantly elevated in muscular dystrophies (500-1500 U/L).
- CK is also elevated in crush injuries, fractures, and cerebrovascular diseases.
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Cardiac Troponins:
- Troponins are not enzymes.
- They are found in cardiac and skeletal muscles, but not in smooth muscles.
- Troponin I is released into the blood within 4 hours of myocardial ischemia.
- Troponin I (TnI) is specific for cardiac disease and its concentration is higher than CK-MB, making it sensitive to cardiac injuries.
- Troponin T (TnT) levels rise within 6 hours of myocardial infarction.
Lactate Dehydrogenase (LDH)
- LDH catalyzes the conversion of pyruvate to lactate.
- There are five LDH isoenzymes, each with different subunits (H for heart and M for muscle).
- LDH-1 (H4) is the fastest in electrophoresis, heat stable, and primarily found in the heart.
- LDH-2 (H3M1) is faster, heat stable, and found in red blood cells.
- LDH-3 (H2M2) is fast, partially degrades with heat, and found in the brain.
- LDH-4 (H1M3) is slower, sensitive to heat, and found in the liver.
- LDH-5 (M4) is the slowest, heat-labile, and found in skeletal muscles.
- Normal serum LDH levels are 100-200 U/L.
- LDH levels are 100 times higher in red blood cells than in plasma.
- Strenuous exercise can slightly increase LDH levels.
- In myocardial infarction, total LDH activity and H4 isoenzyme increase.
- Elevated LDH levels are seen in hemolytic anemias, hepatocellular damage, muscular dystrophy, carcinomas, leukemias, and other conditions causing cell necrosis.
Myoglobin
- An oxygen-binding heme protein found in high concentrations in cardiac and skeletal muscles.
- Released into plasma due to muscle damage.
- Serum myoglobin is directly proportional to muscle mass and can vary with gender, age, and activity.
- Myoglobin is not a long-term marker as it is excreted in urine due to its small size.
- Myoglobin is more sensitive than CK and CK-MB in the first hours after chest pain onset.
- Myoglobin levels begin to rise within 1-4 hours, peak at 6-9 hours, and remain elevated for 18-24 hours.
- CK-MB is preferred for patients admitted to the hospital after 12-14 hours and those with kidney disorders.
Brain Natriuretic Peptide (BNP)
- BNP belongs to a family of peptides that includes ANP and CNP.
- BNP is produced mainly in the cardiac ventricles.
- BNP is secreted by the ventricles in response to stretching of heart muscle cells.
- The inactive form of BNP is pro-BNP, which is converted to BNP in cardiac cells.
- High BNP levels are seen in congestive heart failure and are correlated to ventricular dysfunction.
- Pro-BNP is a good indicator of heart failure severity.
- High BNP levels predict higher mortality rates.
hs-CRP (High Sensitivity C-reactivity Protein)
- hs-CRP measures inflammation in the body.
- High hs-CRP levels are associated with an increased risk of cardiovascular disease.
- Risk levels based on hs-CRP concentration:
- < 1 mg/L: Lowest risk
- 1-3 mg/L: Intermediate risk
-
3 mg/L: Highest risk
Cholinesterase (ChE)
- Acetylcholinesterase (True ChE):
- Found in red blood cells and nerve endings.
- High levels are found in newly formed red blood cells, which decrease with age.
- Pseudocholinesterase (Type II ChE):
- Nonspecific and hydrolyzes acyl esters.
- Produced mainly by liver cells.
- Succinylcholine is a muscle relaxant that is hydrolyzed by liver ChE.
- Deficiency in ChE leads to prolonged paralysis.
- Organophosphate insecticides irreversibly inhibit ChE in red blood cells.
- ChE level measurements in red blood cells can indicate exposure to insecticides.
Causes of Decreased Plasma Cholinesterase Activity
- Hepatic parenchymal disease
- Exposure to anticholinesterases, such as organophosphates
- Inherited abnormal cholinesterase variants with low activity
- Pregnancy
Causes of Increased Plasma Cholinesterase Activity
- Recovery from liver damage
- Nephrotic syndrome
Suxamethonium Sensitivity
- Muscle relaxants, such as suxamethonium and mivacurium, are broken down by plasma cholinesterase.
- Low cholinesterase activity can lead to prolonged apnea (scoline apnea).
- Abnormal cholinesterase variants can be classified by measuring dibucaine number or fluoride number.
- Affected individuals should inform their anesthetist.
Amylase
- Normal serum value is 50-120 IU/L.
- Converts polysaccharides into simple sugars.
- Produced by the pancreas and salivary glands.
- There are three forms of amylase:
- α-amylase: Found in mammals, optimal pH 6-7.
- β-amylase: Found in plants and microorganisms, optimal pH 4-5.
- γ-amylase: Found in animals and microorganisms, works in acidic media (pH 3).
- Amylase levels increase significantly in acute pancreatitis.
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Description
Test your knowledge on enzymes, their functions, and the role of cofactors and coenzymes in biological reactions. This quiz covers topics including enzyme structure, activity conditions, and inhibitors. Challenge yourself and see how well you understand these essential biological catalysts.
