Enzymology in Medicine Quiz

Study Notes

The branch of medicine dealing with the study and application of enzymes in diagnosis and treatment of diseases.

Coenzyme: Organic non-protein biochemical, essential for catalytic activity as a co-substrate. Examples: NAD, Pyridoxal phosphate.
Activator: Inorganic ionic cofactor, key metabolic regulator of enzyme reactions. Examples: Mg++, Ca++, K+, Zn++.
Holoenzyme: Enzyme combined with its cofactor.
Apoenzyme: Enzyme lacking its cofactor.
Prosthetic group: Coenzyme that cannot be separated from the enzyme. Examples: Pyridoxal phosphate in transaminase reaction.

Metalloenzyme: Enzyme with inorganic activators as part of the enzyme molecule.
Substrate: Substance acted upon by an enzyme and converted into a new substance.
Product: The transformed substrate, the result of the enzyme reaction.

Primary structure: The sequence of amino acids linked by peptide bonds forming a polypeptide chain.
Secondary structure: Conformation of polypeptide chain segments. Two common forms: alpha-helix and beta-pleated sheet. Maintained by hydrogen bonding.
Tertiary structure: Arises from interactions between polypeptide chain side chains and groups. Forms a bent and folded structure. Maintained by covalent disulfide bonds.
Quaternary structure: Separate bent and folded structures combined to form a functional unit. Examples: Hemoglobin (4 polypeptide units), enzyme variants (LDH, Creatine kinase).

Based on catalytic activity: Classified into six classes by the International Union of Biochemistry (IUB).
I. Oxidoreductases*
Catalyze oxidation-reduction reactions.
Older names: Dehydrogenases and Oxidases.
Used in investigations of cardiac and liver disorders.
Examples: Glucose oxidase, Cytochrome oxidase, Lactate dehydrogenase, Isocitrate dehydrogenase.
II. Transferases*
Move intact groups of atoms (NH2 or PO4) from one molecule to another.
Used in the laboratory diagnosis of liver and muscle damage.
Examples: Aspartate aminotransferase, Alanine aminotransferase, Creatine kinase.
III. Hydrolases*
Split molecules in the presence of water.
A. Esterases: Examples: ACP, ALP, Lipase.
B. Peptidases: Examples: Leucine aminopeptidase, Pepsin
C. Glycosidases: Examples: Amylase, Amylo-1,6-glucosidase.
IV. Lyases*
Responsible for splitting molecules or breaking bonds (C to C; C to O; C to N, etc.).
Assayed in skeletal muscle disorders.
Examples: Aldolase, Glutamate decarboxylase, Pyruvate decarboxylase.
V. Isomerases*
Enzymes that convert one isomer to another.
Transformations include: Cis to Trans, L to D forms, Aldehyde to Ketone.
All reactions are reversible.
Example: Glucose PO4 Isomerase.
VI. Ligases*
Enzymes that cause bond formation between two molecules to form a larger molecule.
Examples: Ligase, Amino Acyl t-RNA synthetase.

Named based on:
- Type of reaction catalyzed.
- Suffix "-ase" added to the name of the substrate.
Empirical name: Examples: Trypsin, Pepsin.
Standard System (IUB & IUPAC):
- Systematic name: Describes the nature of the reaction catalyzed. Examples: E.C. 3.1.3.1 = ALP, E.C. 3.1.3.2 = ACP. - First digit: Class of the enzyme. - Second digit: Sub-class of the enzyme. - Third digit: Subsub-class. - Fourth digit: Specific serial number.
- Trivial name: Non-specific, practical, working name. A simplification of the systematic name. Examples: SGOT, SGPT.

Isoenzymes: Multichained enzymes with similar activity but tissue/organ and cell organelle specificity. An example is Lactate Dehydrogenase (LDH).

Different forms of enzymes are important for diagnosis.
Isoenzymes are often tissue or cell-specific, and their levels can be used to diagnose different conditions.
For example, measuring different LDH isoenzyme levels can help physicians differentiate between heart and liver damage.