Liver microsomal drug-metabolizing enzyme system: functional components and their properties

Area of Science:

• Biochemistry
• Pharmacology
• Enzymology

Background:

• The liver microsomal drug-metabolizing enzyme system is crucial for xenobiotic detoxification.
• This system comprises key proteins: cytochrome P-450 (CYP) and NADPH-cytochrome c reductase, along with phosphatidylcholine.
• CYP acts as the primary binding site for oxygen and substrates, while the reductase facilitates electron transfer.

Purpose of the Study:

• To elucidate the roles of individual components in the liver microsomal drug-metabolizing enzyme system.
• To investigate the properties of purified cytochrome P-450 and P-448 hemeproteins.
• To understand the basis for inter-individual variations in drug metabolism.

Main Methods:

• Purification of different cytochrome P-450 and P-448 isoforms.
• Characterization of spectral, catalytic, and immunological properties.
• Determination of molecular weights using SDS-gel electrophoresis.

Main Results:

• Purified hemeproteins (cytochrome P-450 and P-448) exhibited distinct spectral, catalytic, and immunological profiles.
• Molecular weights varied among the different purified cytochrome P-450 isoforms.
• Phosphatidylcholine was identified as a facilitator, not a direct electron carrier, in the electron transfer process.

Conclusions:

• The existence of multiple cytochrome P-450 isoforms is a key factor in drug metabolism variability.
• Species, strain, age, tissue, sex, inducers, and nutritional status influence drug metabolism through these diverse CYPs.
• Understanding these multiple forms is essential for predicting and managing drug responses in mammals.