Enzymatic Action and Clinical Enzymology

Vocabulary practice flashcards covering basic enzymology concepts, mechanisms of enzyme action, factors affecting enzyme activity, diagnostic enzymes, clinical applications, and inborn errors of metabolism.

Enzyme

A macromolecule that acts as a biological catalyst to accelerate biochemical reactions.

Substrate

The starting molecule in a chemical reaction upon which an enzyme acts.

Active site

The region on an enzyme that contains one or more binding sites that orient the substrate in the correct configuration.

Catalytic site

The specific portion of an enzyme molecule responsible for lowering activation energy.

Cofactor

A non-protein chemical compound or metallic ion (such as metal ions or vitamins) required for an enzyme's activity.

Lock and Key Theory

A model postulated in 1894 by Emil Fischer stating that the enzyme acts as a lock and the substrate as a key, where only a correctly shaped substrate fits into the active site.

Induced Fit Theory

A model assuming that the substrate helps determine the final shape of the enzyme and that the enzyme active site is partially flexible.

Photolyase

An enzyme involved in photoreactivation DNA repair that requires light for its catalytic activity.

Diagnostic enzymes

Enzymes used directly or as assay components to determine concentrations of biomolecules for identifying metabolic abnormalities or disease states.

Lactate Dehydrogenase (LDH)

An enzyme involved in glucose metabolism found throughout the body, with a normal range of $180\text{--}360\text{ U/L}$.

LDH1

An isoenzyme of lactate dehydrogenase found predominantly in heart muscle and red blood cells.

LDH5

An isoenzyme of lactate dehydrogenase found in liver and skeletal muscle that is the least stable and migrates the shortest distance during electrophoresis.

LDH3

An isoenzyme of lactate dehydrogenase found in tissues including the spleen, lungs, endocrine glands, and lymph nodes.

Aspartate Transaminase (AST)

An enzyme formally known as glutamate oxaloacetate transaminase (GOT), elevated levels of which indicate myocardial infarction or tissue damage (normal range: male $<35\text{ U/L}$, female $<31\text{ U/L}$).

Alanine Transaminase (ALT)

An enzyme formally known as glutamate-pyruvate transaminase (GPT), found in high concentrations in liver cells; markedly raised levels indicate severe liver disease such as viral hepatitis or toxic liver necrosis (normal range: male $<45\text{ U/L}$, female $<34\text{ U/L}$).

Alkaline Phosphatase (ALP)

An enzyme found in high levels in the liver, bone, placenta, and intestine, commonly used as a diagnostic marker for cholestatic liver disease.

Cholestatic liver disease

A condition resulting from impairment in bile formation or flow, clinically characterized by fatigue, pruritus, and jaundice.

Creatine Kinase (CK)

An enzyme also known as creatine phosphokinase (CPK) present in heart, skeletal muscle, and brain (normal range: male $46\text{--}171\text{ U/L}$, female $34\text{--}145\text{ U/L}$).

CKBB

The predominant isoenzyme form of creatine kinase present in the brain.

CKMB

The isoenzyme form of creatine kinase found in heart muscle and the diaphragm.

CKMM

The isoenzyme form of creatine kinase present in both skeletal muscle and heart muscle.

Acid Phosphatase

An enzyme with its richest source in the prostate gland used in plasma assays for diagnosing prostatic carcinoma; also present in liver, RBCs, platelets, bone, and lysosomes (normal range: $0.1\text{--}0.4\text{ U/L}$).

Cholinesterase

An enzyme assayed prior to administering the muscle relaxant scoline to prevent severe breathing difficulties in patients with low activity (normal range: male $40\text{--}78\text{ U/L}$, female $33\text{--}76\text{ U/L}$).

gamma-Glutamyl Transferase (GGT)

An enzyme present in biliary ducts, kidneys, pancreas, and hepatocytes; induced by alcohol and used as a marker for alcohol-induced liver disease and cirrhosis.

Amylase

An enzyme produced in high concentrations by the pancreas and salivary glands to digest complex carbohydrates, used clinically to differentiate acute pancreatitis from appendicitis (normal range: $28\text{--}100\text{ U/L}$).

Inborn error of metabolism

An inherited pathological condition in which a specific enzyme is deficient or lacks full activity.

Phenylketonuria

An inborn error of metabolism caused by a deficiency in the enzyme Phenylalanine hydroxylase.

Alkaptonuria

An inborn error of metabolism caused by a deficiency in the enzyme Homogenitisic acid oxidase.

Galactosaemia

An inborn error of metabolism caused by a deficiency in the enzyme galactokinase.

Von Gierke's disease

An inborn error of metabolism caused by a deficiency in the enzyme Glucose-6-phosphatase.

Tay-Sachs disease

An inborn error of metabolism caused by a deficiency in the enzyme B-N-Acetyl glucosaminidase A.

Hurler's syndrome

An inborn error of metabolism caused by a deficiency in the enzyme A-L- Iduronidase.

Glucose Oxidase

An enzyme used as a clinical reagent to analyze D-glucose in body fluids and urine specimens for diagnosing Diabetes Mellitus.

Cholesterol Oxidase

An enzyme reagent used to catalyze reactions for measuring blood cholesterol levels.