Clinical Enzymology Quiz

Clinical Enzymology

• Apoenzyme: The protein portion of an enzyme without its cofactor.
• Activator: A molecule that increases an enzyme's activity by binding to it. Can be organic (like NAD/NADH) or inorganic (electrolyte).
• Inhibitor: A substance that reduces the rate of enzymatic reactions. It binds to the active site or allosteric site.
• Active site: The region where a substrate binds to an enzyme.
• Allosteric site: A different region of an enzyme other than the active site where regulatory molecules bind.
• Catalytic activity: An enzyme's ability to speed up biochemical reactions.
• Coenzyme: A low molecular weight, diffusible, heat-stable substance that combines with an inactive protein (apoenzyme) to form an active compound (holoenzyme).
• Enzyme: A protein molecule that accelerates chemical reactions without being consumed itself. Specific for a substrate. Large molecules typically located inside cells. They're released into the blood after cellular injury and degradation.
• Isoenzyme: Related enzymes that catalyze the same reaction, but with different structures and physical, biochemical, and immunological properties.
• International unit (IU): A standard unit of enzyme measurement. Also expressed as Katal.
• Substrate: A reactant in a biochemical reaction.
• Product: A substance produced by an enzyme-catalyzed reaction.

Enzyme Theories

• Emil Fischer's "Lock and Key" Theory: Enzymes have rigid active sites, and the substrate shape must precisely fit.
• Koshland's "Induced Fit" Theory: Enzymes have flexible active sites that adjust their shape to accommodate the substrate.

Enzyme Kinetics

• Activation energy: The minimum energy needed for a reaction to proceed.
• Transition state: The intermediate stage between substrate and product during a catalyzed reaction.
• Zero-order reaction: Reaction rate depends only on enzyme concentration.
• First-order reaction: Reaction rate is directly proportional to substrate concentration.

Enzyme Specificity

• Absolute specificity: Enzymes combine with only one substrate and catalyze only one reaction.
• Group specificity: Enzymes combine with any substrate within a specific chemical group (e.g., all alcohols).
• Bond specificity: Enzymes react with specific chemical bonds (e.g., ionic, covalent, ester bonds).

Enzyme Classification

• Oxidoreductases: Catalyze oxidation-reduction reactions.
• Transferases: Catalyze the transfer of functional groups.
• Hydrolases: Use water to break down bonds.
• Lyases: Catalyze reactions that remove groups from molecules
• Isomerases: Catalyze structural changes within a molecule.
• Ligases: Combine molecules through bonds.

Enzyme Nomenclature

• Systematic name: Describes the nature of the reaction catalyzed by the enzyme.
• Numerical nomenclature: Associated with a unique numerical code (EC).

Enzyme Activity Measurement

• Fixed-time (Endpoint) Method: Measures the concentration of products at a specific time point during a reaction
• Continuous Monitoring (Kinetic Assay): Measures reaction rate during the reaction, providing ongoing measurements of product formation or substrate consumption.

Units for Enzyme Activity

• International Unit (IU): Amount of enzyme that catalyzes 1 micromole of substrate per minute.
• Katal (kat): Amount of enzyme that catalyzes 1 mole of substrate per second.

Liver Enzymes and Liver Function Tests

• AST (Aspartate aminotransferase): Enzyme found in various tissues, including the liver and heart. Elevated levels can indicate liver damage.
• ALT (Alanine aminotransferase): Primarily found in the liver. Elevated levels strongly suggest liver injury.
• Other liver specific markers: These other enzymes can be associated with obstructive jaundice.

Cardiac Markers

• Troponin I and T: Highly specific markers for myocardial damage. Elevated levels indicate a heart attack.
• Creatine kinase (CK): Enzyme released from damaged muscle cells, especially the heart, but widely distributed in tissues.
• Lactate dehydrogenase (LD): Enzyme found in many tissues, including the heart. Elevated levels can indicate heart attack or other conditions.
• Other markers: Myoglobin, H-FABP, IMA (Ischemia-Modified Albumin) may have uses in cardiac diagnosis.

Alkaline Phosphatase (ALP)

• Hydrolase (EC 3.1.3.1): Enzyme involved in the hydrolysis of phosphate monoesters, mainly in the liver, bone, and intestine.
• Clinical Significance: Elevated levels may suggest skeletal, liver or intestinal conditions, such as obstructive jaundice or bone diseases.

Acid Phosphatase (ACP)

• Hydrolase (EC 3.1.3.2): Enzyme that hydrolyzes phosphate groups from organic phosphate compounds, found typically in various tissues and cells.
• Clinical Significance: Elevated levels may be associated with certain cancers and other illnesses.

Other Clinically Significant Enzymes

• Amylase: Enzyme that breaks down carbohydrates (starch, glycogen); elevated levels can suggest pancreatitis (inflammation of the pancreas).
• Lipase: Enzyme that breaks down lipids; elevated levels are highly specific for pancreatic damage.
• Gamma-glutamyl transferase (GGT): Enzyme indicating liver damage or blockage of bile ducts; useful in monitoring chronic alcohol use.
• Glucose-6-Phosphate Dehydrogenase (G6PD): Enzyme important for protecting red blood cells from oxidative stress.