Final answer:
The enzyme responsible for most drug biotransformation in the liver is cytochrome P450. This group of enzymes is key to hepatic metabolism, modifying substances to make them more excretable. The correct answer to the student's question is b. cytochrome P450.
Step-by-step explanation:
The majority of drug biotransformation in the liver is accomplished by a family of enzymes known as cytochrome P450 (CYP). These CYP enzymes play a crucial role in the metabolism of various substances, including drugs, where they catalyze reactions that make these substances more soluble and excretable. Each isoform of the CYP enzyme contributes differently to the total hepatic clearance, making it essential to identify the relative contribution of each isoform in drug metabolism.
For instance, different drugs and toxins are processed through specific CYP isoforms, such as the metabolism of ethanol via the alcohol dehydrogenase system, where ethanol is first converted to acetaldehyde and then acetaldehyde dehydrogenase converts acetaldehyde into acetate, a non-toxic molecule. This process illustrates the complex nature of hepatic metabolism and the essential role that CYP enzymes play in detoxifying harmful substances and preparing them for excretion.
When it comes to drug development, it is crucial to assess the in vitro metabolism by CYP isoforms in the human liver S9 fraction, utilizing specific inhibitors for each isoform to ascertain their roles. As such, non-CYP mediated conversion can sometimes be desirable due to the polymorphism seen with CYP-mediated pathways, which affects both efficacy and toxicity of drugs.
Given the options provided, the student's question refers to the enzyme responsible for the majority of drug biotransformation in the liver and the correct option is b. cytochrome P450.