Enzymes: Classification of Enzymes

oxidoreductase

transfer elctrons or H atoms

xanthine oxidase

an oxidoreductase that Converts hypoxanthine → xanthine → uric acid.

xanthine oxidase hyperactivity

________________ → hyperuricemia & gout

allopurinol

competitive inhibitor of xanthine oxidase

Lactate Dehydrogenase (LDH)

an oxidoreduc tase that Converts lactate to pyruvate.

Marker: ↑ in hemolysis, MI, liver disease, some cancers.

Cytochrome P450 enzymes (CYPs)

• an oxidoreductase that Metabolize drugs in liver

• Variability in CYP activity affects drug dosing, toxicity, resistance.

Glucose-6-Phosphate Dehydrogenase (G6PD)

• an oxidoreductase that Produces NADPH in RBCs.

• Deficiency → hemolytic anemia when exposed to oxidative stress (e.g., fava beans, sulfa drugs).

• xanthine oxidase

• lactate dehydrogenase

• cytochrome P450 enzymes (CPYs)

• Glucose-6-Phosphate Dehydrogenase (G6PD)

Examples of oxidoreductases

transferase

transfer groups to other m molecules

AST & ALT

transferase:
Markers: ↑ in hepatitis, liver injury, MI (AST also in heart).

GGT

transferase:

Marker: ↑ in alcoholic liver disease, cholestasis.

CK & CK-MB

transferase:

Marker: ↑ in myocardial infarction, muscular dystrophies

• AST

• ALT

• GGT

• CK & CK-MB

• peptidyl transferase

examples of transferases

hydrolase

breaks molecules apart with water (hydrolysis reaction)

Amylase & Lipase

hydrolase:

• Digest starches and lipids

• Markers: ↑ in acute pancreatitis

acetylcholinesterase

hydrolase:

• Breaks down acetylcholine → choline + acetic acid in synapses.

• ensures stimuli are brief and controlled

organophosphates

acetylcholinesterase is inhibited by ______________ → cholinergic crisis

myasthenia gravis

Drugs inhibit acetylcholinestarease to treat ______________

cholinergic crisis

• caused by an excess of the neurotransmitter acetylcholine (ACh) at nerve and muscle junctions, leading to overstimulation of cholinergic receptors

• due to inhibition of acetylcholinesterase

• life threatening

Acid phosphatase (ACP)

hydrolase:

 Marker: ↑ in prostate carcinoma (historical use), bone diseases.

• amylase

• lipase

• acetylcholinesterase

• acid phosphatase (ACP)

examples of hydrolases

lyase

• addition, transfer, or removal of groups to double bonds

• non-hydrolytic transfer of groups

pyruvate decarboxylase

lyase:
Involved in metabolism (lab teaching).

histidine ammonia-lyase

Disease link: Deficiency → histidinemia, a rare inherited metabolic disorder

• arginosuccinate lyase

• pyruvate decarboxylase

• histidine ammonia-lyase

examples of lyase

isomerase

transfer of functional group/s within molecules

change sthe structure/ isomeric form

Phosphoglucose isomerase (PGI)

isomerase:
Glycolysis (glucose-6- phosphate fructose-6-phosphate).

Clinical note: Deficiency → nonspherocytic hemolytic anemia.

Triosephosphate Isomerase (TPI)

isomerase:

Clinical note: Rare * deficiency → progressive neuromuscular disorder.

• phosphoglucose isomerase (PGI)

• triosephosphate isomerase (TPI)

examples of isomerase

ligase

combines/ysnthesizes molecules through condensation reactions

DNA ligase

ligase:

• repairs DNA strand break

immunodeficiency & cancer

defects in DNA ligase → predisposition to ______________ and __________

glutamine synthetase

ligase:

• glutamate + ammonia + ATP → glutamine

• nitrogen assimilation and ammonia detoxification in brain

hepatic encephalopathy

• dysregulation of Glutamate synthetase is linked to ______________

• leads to brain dysfunction due to liver dysfunction

• subtle cognitive changes to severe confusion, personality alterations, disorientation, lethargy, and coma.

• DNA ligase

• Glutamine synthetase

examples of ligases

1. oxidoreductases

2. transferases

3. hydrolases

4. lyases

5. isomerases

6. ligases (synthetases)

List the 6 classifications of enzymes in chronological (IUPAC)