Drug Metabolism: Phase I and Phase II

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Questions and Answers

Which reaction is an example of oxidation?

Conversion of CH₃CH₂OH to CH₃CH₂COOH (correct)
Conversion of COOH to CH₃
Conversion of NH₂ to N₂
Formation of ester from COOH and OH

What is the product of hydrolysis of ester?

CH₃ and COOH
COOH and NH₂
NH₂ and OH
COOH and OH (correct)

What is the resulting functional group from the reduction of azo and nitro compounds?

NH₂ (correct)
COOH
CH₃
OH

What is the opposite reaction of hydrolysis of ester?

Esterification reaction (D) Signup and view all the answers

What is the primary purpose of phase I drug metabolism reactions?

To introduce a functional polar group into the xenobiotic molecule (D) Signup and view all the answers

What is the common feature among these reactions: oxidation of alcohols to acids, hydrolysis of ester and amides, and reduction of azo and nitro compounds?

All involve the breaking or formation of functional groups (C) Signup and view all the answers

Which of the following is NOT a type of phase I biotransformation reaction?

Conjugation reaction (D) Signup and view all the answers

What is the result of introducing a functional polar group into a xenobiotic molecule?

Increased water solubility of the xenobiotic molecule (C) Signup and view all the answers

What is the ultimate goal of phase I and phase II drug metabolism reactions?

To facilitate the excretion of the xenobiotic molecule (C) Signup and view all the answers

Which of the following is an example of a functional polar group introduced during phase I drug metabolism reactions?

Hydroxyl group (C) Signup and view all the answers

What is the primary difference between phase I and phase II drug metabolism reactions?

Phase I reactions introduce functional polar groups, while phase II reactions conjugate the xenobiotic molecule (B) Signup and view all the answers

What does the number in a cytochrome notation specify?

The family of the cytochrome (B) Signup and view all the answers

What is the purpose of the capital letter in a cytochrome notation?

To specify the subfamily of the cytochrome (D) Signup and view all the answers

What is the relationship between CYP1 and CYP1A?

CYP1 is a family and CYP1A is a subfamily (A) Signup and view all the answers

What do CYP2A and CYP2B have in common?

They belong to the same family (C) Signup and view all the answers

What is the difference between CYP1B and CYP2B?

They belong to different families (C) Signup and view all the answers

What is the general naming convention for cytochrome enzymes?

CYP- enzyme number - family number (C) Signup and view all the answers

What is the significance of the number at the end of the cytochrome name?

It specifies the specific enzyme responsible for a particular reaction (C) Signup and view all the answers

What is the common prefix for all cytochrome enzymes?

CYP (B) Signup and view all the answers

What is the purpose of the numbering system for cytochrome enzymes?

To identify the specific enzyme responsible for a particular reaction (A) Signup and view all the answers

What is the term for the family of enzymes that includes CYP1A2, CYP2C9, and CYP2C19?

Cytochrome P450 family (A) Signup and view all the answers

What is the role of molecular oxygen in the mixed-function oxidase system?

To oxidize the substrate RH (A) Signup and view all the answers

What is the superfamily of enzymes responsible for transferring an oxygen atom to the substrate RH?

CYP oxidase (B) Signup and view all the answers

What is the reducing agent required in the mixed-function oxidase system?

NADPH (A) Signup and view all the answers

What is the function of the NADPH-dependent CYP reductase?

To supply reducing equivalents to the CYP enzymes (A) Signup and view all the answers

What is the name of the heme portion of the CYP enzyme?

Protoporphyrin IX (A) Signup and view all the answers

Where is the CYP enzyme found in high concentrations?

Liver (C) Signup and view all the answers

What is the significance of the presence of CYP enzyme in other tissues?

These tissues have drug-oxidizing capability (D) Signup and view all the answers

What is the wavelength at which the reduced form of CYP enzyme has a distinguishing spectroscopic absorption maximum?

450 nm (C) Signup and view all the answers

What is formed when the reduced form of CYP enzyme binds with carbon monoxide?

A complex with a spectroscopic absorption maximum at 450 nm (B) Signup and view all the answers

What is the name of the enzyme system that requires both molecular oxygen and NADPH?

Mixed-function oxidase system (A) Signup and view all the answers

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Study Notes

General Pathways of Drug Metabolism

Drug metabolism reactions are divided into two categories: phase I (functionalization) and phase II (conjugation) reactions.

Phase I (Functionalization) Reactions

Include oxidative, reductive, and hydrolytic biotransformations.
Introduce a functional polar group(s) (e.g., OH, COOH, NH2, SH) into the xenobiotic molecule to produce a more water-soluble compound.
Achieved through:
- Oxidation of alcohols to acids.
- Hydrolysis of ester and amides to yield COOH, NH2, and OH groups.
- Reduction of azo and nitro compounds to give NH2 moieties.

Cytochrome P450 (CYP) Enzymes

CYP enzymes are heme + proteins.
The heme portion is an iron-containing porphyrin called protoporphyrin IX.
The protein is called the apoprotein.
CYP is found in high concentrations in the liver (the major organ involved in the metabolism of xenobiotics).
Also present in other tissues (e.g., lung, kidney, intestine, skin, placenta, adrenal cortex) with drug-oxidizing capability.

Oxidation Reaction

Requires both molecular oxygen and the reducing agent NADPH (reduced form of nicotinamide adenosine dinucleotide phosphate).
One atom of molecular oxygen (O2) is introduced into the substrate R-H to form R-OH.
The other oxygen atom is incorporated into water.
The reaction is catalyzed by the mixed-function oxidase system, which includes:
- CYP oxidase enzymes responsible for transferring an oxygen atom to the substrate RH.
- NADPH-dependent CYP reductase.
- NADH-linked cytochrome b5.

NADPH and NADH

Supply the reducing equivalents (electrons) needed in the overall metabolic oxidation of foreign compounds.
Help maintain the chemical balance of the reaction by providing the necessary electrons for reduction.

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