Introduction: Phase II metabolism involves conjugation reactions that transform drug molecules into more water-soluble derivatives for excretion. B. Pharm students must master conjugating enzymes such as UDP-glucuronosyltransferases (UGTs), sulfotransferases (SULTs), glutathione S-transferases (GSTs), N-acetyltransferases (NATs) and methyltransferases, along with their cofactors (UDPGA, PAPS, GSH, Acetyl-CoA, SAM). Understanding substrate specificity, enzyme location, genetic polymorphisms (e.g., NAT2, UGT1A1), clinical consequences (bilirubin handling, drug interactions, toxicity) and analytical detection (LC-MS) is essential for pharmacokinetics, dosage design and safety assessment. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. Which is the primary purpose of Phase II (conjugation) metabolism?
- To increase lipid solubility of drugs
- To decrease water solubility of drugs
- To increase water solubility of drugs for excretion
- To convert prodrugs into active metabolites
Correct Answer: To increase water solubility of drugs for excretion
Q2. Which cofactor is required for glucuronidation reactions?
- PAPS (3′-phosphoadenosine-5′-phosphosulfate)
- UDP-glucuronic acid (UDPGA)
- S-adenosylmethionine (SAM)
- Glutathione (GSH)
Correct Answer: UDP-glucuronic acid (UDPGA)
Q3. Which enzyme family catalyzes sulfation reactions in Phase II metabolism?
- CYP450 monooxygenases
- Sulfotransferases (SULTs)
- UDP-glucuronosyltransferases (UGTs)
- Glutathione S-transferases (GSTs)
Correct Answer: Sulfotransferases (SULTs)
Q4. Glutathione conjugation primarily protects cells by reacting with:
- Hydrophilic drugs to increase absorption
- Reactive electrophilic metabolites and free radicals
- Conjugated bilirubin to form glucuronides
- Polar carbohydrates to form glycosides
Correct Answer: Reactive electrophilic metabolites and free radicals
Q5. Which enzyme catalyzes acetylation in Phase II metabolism and is known for genetic polymorphism?
- UDP-glucuronosyltransferase 1A1 (UGT1A1)
- N-acetyltransferase (NAT)
- Sulfotransferase 1A1 (SULT1A1)
- Glutathione S-transferase Mu (GSTM)
Correct Answer: N-acetyltransferase (NAT)
Q6. Which Phase II enzyme is primarily located in the endoplasmic reticulum membrane of hepatocytes?
- UDP-glucuronosyltransferases (UGTs)
- Sulfotransferases (SULTs)
- Glutathione S-transferases (GSTs)
- Methyltransferases
Correct Answer: UDP-glucuronosyltransferases (UGTs)
Q7. The cofactor PAPS is required for which conjugation pathway?
- Glucuronidation
- Sulfation
- Glutathione conjugation
- Methylation
Correct Answer: Sulfation
Q8. Which conjugation pathway uses S-adenosylmethionine (SAM) as methyl donor?
- Methylation
- Glucuronidation
- Sulfation
- Glutathione conjugation
Correct Answer: Methylation
Q9. Which Phase II reaction commonly forms N-acetylated metabolites and affects isoniazid toxicity?
- Glucuronidation by UGTs
- Acetylation by NATs
- Sulfation by SULTs
- Glutathione conjugation by GSTs
Correct Answer: Acetylation by NATs
Q10. Which genetic variant is associated with reduced glucuronidation of bilirubin and Gilbert’s syndrome?
- UGT1A1*28 polymorphism
- NAT2 slow acetylator genotype
- SULT1A1 gene duplication
- GSTM1 null variant
Correct Answer: UGT1A1*28 polymorphism
Q11. Enterohepatic recycling of drugs often involves which Phase II metabolite?
- Glucuronide conjugates
- Sulfate conjugates
- Acetylated metabolites
- Methylated derivatives
Correct Answer: Glucuronide conjugates
Q12. Which analytical technique is most suitable to identify Phase II metabolites in biological samples?
- Thin-layer chromatography only
- LC-MS/MS (liquid chromatography–tandem mass spectrometry)
- Simple UV spectrophotometry
- Light microscopy
Correct Answer: LC-MS/MS (liquid chromatography–tandem mass spectrometry)
Q13. Which conjugation increases polarity by adding glucuronic acid?
- Glucuronidation
- Sulfation
- Methylation
- Acetylation
Correct Answer: Glucuronidation
Q14. Which Phase II enzyme family catalyzes conjugation with glutathione (GSH)?
- UGTs
- SULTs
- GSTs (glutathione S-transferases)
- NATs
Correct Answer: GSTs (glutathione S-transferases)
Q15. Which statement about Phase II metabolism is correct?
- Phase II reactions always precede Phase I reactions
- Phase II reactions generally decrease molecular weight
- Phase II reactions often follow Phase I to increase excretion
- Phase II reactions exclusively occur in plasma
Correct Answer: Phase II reactions often follow Phase I to increase excretion
Q16. Which substrate functional group is least likely to undergo direct glucuronidation?
- Hydroxyl group
- Carboxylic acid
- Primary amine without prior modification
- Phenolic OH
Correct Answer: Primary amine without prior modification
Q17. Mercapturic acid formation involves which sequence?
- Glucuronidation → methylation → excretion
- GSH conjugation → processing → N-acetylcysteine (mercapturic acid)
- Sulfation → glucuronidation → excretion
- Acetylation → methylation → excretion
Correct Answer: GSH conjugation → processing → N-acetylcysteine (mercapturic acid)
Q18. Which Phase II enzyme can be induced by nuclear receptors like PXR affecting drug clearance?
- UGTs (UDP-glucuronosyltransferases)
- GSTs only
- All SULT isoforms equally
- Methyltransferases exclusively
Correct Answer: UGTs (UDP-glucuronosyltransferases)
Q19. Which conjugation can paradoxically increase lipophilicity in some cases, reducing renal excretion?
- Glucuronidation of small polar acids
- Amino acid conjugation forming bulky acyl amino acids
- Sulfation always increases hydrophilicity
- Methylation always increases water solubility
Correct Answer: Amino acid conjugation forming bulky acyl amino acids
Q20. N-glucuronidation differs from O-glucuronidation by conjugating to which atom?
- N-glucuronidation attaches to nitrogen; O-glucuronidation attaches to oxygen
- N-glucuronidation attaches to oxygen; O-glucuronidation attaches to nitrogen
- Both attach only to sulfur
- There is no difference; terms are interchangeable
Correct Answer: N-glucuronidation attaches to nitrogen; O-glucuronidation attaches to oxygen
Q21. Which cofactor is directly consumed in sulfation reactions?
- UDPGA
- PAPS
- SAM
- ATP
Correct Answer: PAPS
Q22. Which clinical condition results from impaired bilirubin glucuronidation?
- Phenylketonuria
- Gilbert’s syndrome and Crigler–Najjar syndromes
- Lactose intolerance
- Hemophilia
Correct Answer: Gilbert’s syndrome and Crigler–Najjar syndromes
Q23. Which Phase II reaction is most likely to deactivate catecholamines pharmacologically?
- Glucuronidation
- Sulfation
- Methylation by catechol-O-methyltransferase (COMT)
- Glutathione conjugation
Correct Answer: Methylation by catechol-O-methyltransferase (COMT)
Q24. Which pathway commonly uses glycine as conjugating partner for aromatic acids?
- Glucuronidation
- Amino acid conjugation (glycine conjugation)
- Sulfation
- Methylation
Correct Answer: Amino acid conjugation (glycine conjugation)
Q25. Which genetic polymorphism affects isoniazid acetylation rate and toxicity risk?
- UGT1A1*28
- NAT2 slow and rapid acetylator alleles
- SULT1A1*2 duplication
- GSTP1 Ile105Val only
Correct Answer: NAT2 slow and rapid acetylator alleles
Q26. Which Phase II enzyme family contributes to detoxification of electrophiles and peroxides in extrahepatic tissues?
- UGTs
- GSTs (glutathione S-transferases)
- SULTs
- NATs
Correct Answer: GSTs (glutathione S-transferases)
Q27. Which parameter best describes enzyme affinity in conjugation reactions?
- Vmax only
- Km (Michaelis constant)
- Intrinsic clearance unrelated to Km
- pH value of the medium
Correct Answer: Km (Michaelis constant)
Q28. Which drug interaction mechanism can decrease glucuronidation rates?
- Induction of UGT enzymes by another drug
- Competitive inhibition of UGTs by co-administered substrate
- Increased renal blood flow only
- Activation of SULT enzymes exclusively
Correct Answer: Competitive inhibition of UGTs by co-administered substrate
Q29. Which Phase II reaction is reversible under action of bacterial enzymes in the gut leading to reactivation?
- Methylation
- Glucuronidation followed by beta-glucuronidase-mediated deconjugation
- Acetylation irreversible
- Glutathione conjugation reversible by hydrolysis
Correct Answer: Glucuronidation followed by beta-glucuronidase-mediated deconjugation
Q30. Which conjugation tends to be more significant at low substrate concentrations due to high affinity?
- Sulfation (often high affinity, low capacity)
- Glucuronidation (low affinity, high capacity)
- Methylation always low affinity
- Glutathione conjugation independent of concentration
Correct Answer: Sulfation (often high affinity, low capacity)
Q31. Which analytical biomarker indicates glutathione pathway activity in urine?
- Urinary glucuronide levels
- Mercapturic acids (N-acetylcysteine conjugates)
- Sulfate conjugate concentration
- Unchanged parent drug only
Correct Answer: Mercapturic acids (N-acetylcysteine conjugates)
Q32. Which enzyme family catalyzes O-methylation of catechols?
- CYP3A4
- Catechol-O-methyltransferase (COMT)
- UGT1A enzymes
- NAT enzymes
Correct Answer: Catechol-O-methyltransferase (COMT)
Q33. Which Phase II reaction commonly uses Acetyl-CoA as the acetyl donor?
- N-acetylation by NAT enzymes
- Glucuronidation by UGTs
- Sulfation by SULTs
- Methylation by methyltransferases
Correct Answer: N-acetylation by NAT enzymes
Q34. Which factor most directly affects tissue-specific expression of conjugating enzymes?
- Dietary carbohydrate only
- Genetic regulation and organ-specific expression patterns
- Ambient temperature
- Color of medication
Correct Answer: Genetic regulation and organ-specific expression patterns
Q35. Which UGT isoform is primarily responsible for bilirubin conjugation?
- UGT2B7
- UGT1A1
- UGT1A4 only
- GSTM1
Correct Answer: UGT1A1
Q36. Which statement about methylation as a Phase II reaction is true?
- Methylation always increases water solubility significantly
- Methylation often decreases polarity and can inactivate drugs
- Methylation uses UDPGA as cofactor
- Methylation forms mercapturic acids
Correct Answer: Methylation often decreases polarity and can inactivate drugs
Q37. A drug that depletes glutathione (GSH) could increase toxicity from which class of metabolites?
- Inert glucuronides
- Reactive electrophilic metabolites
- Simple sulfates
- Methylated inactive metabolites
Correct Answer: Reactive electrophilic metabolites
Q38. Which process converts a Phase II glucuronide back to the parent compound in the intestine?
- Hepatic sulfation
- Beta-glucuronidase activity from gut bacteria
- UGT catalysis in lumen
- Sulfatase in plasma
Correct Answer: Beta-glucuronidase activity from gut bacteria
Q39. Which drug property most strongly predicts likelihood of glucuronidation?
- High basicity only
- Presence of a suitable nucleophilic functional group (e.g., OH, COOH, NH)
- Large molecular weight exclusively
- Fluorescence under UV light
Correct Answer: Presence of a suitable nucleophilic functional group (e.g., OH, COOH, NH)
Q40. Which conjugation reaction is most likely to be saturated at therapeutic doses for many drugs?
- Glucuronidation (usually high capacity)
- Sulfation (often low capacity and easily saturated)
- Methylation (never saturable)
- Glutathione conjugation (independent of dose)
Correct Answer: Sulfation (often low capacity and easily saturated)
Q41. Which Phase II enzyme commonly conjugates morphine to produce an active metabolite?
- SULT1A1 producing morphine sulfate
- UGT2B7 producing morphine-6-glucuronide
- NAT producing morphine acetate
- GST producing morphine-GSH conjugate
Correct Answer: UGT2B7 producing morphine-6-glucuronide
Q42. Which population variability factor is critically important in dosing drugs cleared by Phase II pathways?
- Genetic polymorphisms of conjugating enzymes
- Color of patient’s hair
- Ambient humidity where patient lives
- Patient’s shoe size
Correct Answer: Genetic polymorphisms of conjugating enzymes
Q43. Which Phase II enzyme is known for gene deletion variants leading to null activity in some individuals?
- UGT1A1 deletion common worldwide
- GSTM1 deletion (null genotype)
- SULT1A1 deletion in all populations
- NAT genes are never deleted
Correct Answer: GSTM1 deletion (null genotype)
Q44. Which conjugation is typically assessed by measuring urinary sulfate conjugates?
- Glutathione conjugation
- Sulfation
- Glucuronidation
- Methylation
Correct Answer: Sulfation
Q45. Which mechanism explains why some Phase II metabolites are excreted into bile rather than urine?
- High hydrophilicity always favors biliary excretion
- Larger molecular size and amphipathicity promote biliary excretion
- Only parent drugs are secreted into bile
- Methylated small molecules exclusively go to bile
Correct Answer: Larger molecular size and amphipathicity promote biliary excretion
Q46. Which drug example illustrates enterohepatic recycling due to glucuronidation and deconjugation?
- Acetaminophen never undergoes enterohepatic cycling
- Estrogens and some NSAIDs show enterohepatic recycling
- Aminoglycosides are glucuronidated and recycled
- Insulin is glucuronidated and recycled
Correct Answer: Estrogens and some NSAIDs show enterohepatic recycling
Q47. Which laboratory approach helps determine if a metabolite is a Phase II conjugate?
- Increase pH only
- Treat sample with beta-glucuronidase or sulfatase and observe increase in parent drug
- Run PCR for UGT genes directly on plasma
- Measure blood pressure changes
Correct Answer: Treat sample with beta-glucuronidase or sulfatase and observe increase in parent drug
Q48. Which statement about conjugation and pharmacological activity is correct?
- All conjugates are pharmacologically inactive
- Some conjugates retain or gain activity (e.g., morphine-6-glucuronide)
- Conjugation always forms toxic products
- Conjugation never affects receptor binding
Correct Answer: Some conjugates retain or gain activity (e.g., morphine-6-glucuronide)
Q49. Which enzyme system primarily handles bilirubin conjugation and impacts neonatal jaundice?
- GSTs in the kidney
- UGT1A1 in the liver
- SULTs in the lungs
- COMT in the brain
Correct Answer: UGT1A1 in the liver
Q50. For designing safer drugs, which Phase II consideration is most important during lead optimization?
- Avoiding functional groups that cannot be conjugated, increasing potential bioactivation and toxicity
- Ensuring the drug cannot be metabolized at all
- Maximizing lipophilicity to prevent excretion
- Designing molecules with no polar groups to avoid conjugation
Correct Answer: Avoiding functional groups that cannot be conjugated, increasing potential bioactivation and toxicity
