Question

NADPH-cytochrome P450 reductase A. uses both FAD and FMN as prosthetic groups. B. binds to cytochrome \(P 450\) by strong hydrophobic interactions. C. requires an iron-sulfur center for activity. D. always passes its electrons to cytochrome bs. E. can use NADH as readily as NADPH.

Short answer

(Choose two) A: It uses both FAD and FMN as prosthetic groups. B: It binds to cytochrome P450 by strong hydrophobic interactions. C: It requires an iron-sulfur center for activity. D: It always passes its electrons to cytochrome bs. E: It can use NADH as readily as NADPH. Answer: A and B

Step-by-step solution

Option A - uses both FAD and FMN as prosthetic groups

NADPH-cytochrome P450 reductase is a flavoprotein that contains both flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) as prosthetic groups. These cofactors play crucial roles in the transfer of electrons from NADPH to cytochrome P450. So, option A is correct.

Option B - binds to cytochrome \(P 450\) by strong hydrophobic interactions

NADPH-cytochrome P450 reductase binds to cytochrome P450 by strong hydrophobic interactions. It forms a transient complex with cytochrome P450 to transfer electrons for the catalytic activity of cytochrome P450 enzymes. So, option B is also correct.

Option C - requires an iron-sulfur center for activity

NADPH-cytochrome P450 reductase does not require an iron-sulfur center for its activity. Instead, it has FAD and FMN prosthetic groups which play important roles in electron transfer. So, option C is incorrect.

Option D - always passes its electrons to cytochrome bs

NADPH-cytochrome P450 reductase is known to transfer electrons mainly to cytochrome P450 enzymes, but it also passes electrons to other proteins like cytochrome b5. Therefore, option D is incorrect as it does not always pass its electrons to cytochrome bs.

Option E - can use NADH as readily as NADPH

NADPH-cytochrome P450 reductase shows a strong preference for using NADPH as an electron donor, as it is a more effective reducing agent. Although it can utilize NADH, the activity is significantly lower and less efficient. Therefore, option E is incorrect. Based on the analysis of each option, we conclude that Option A and B are correct statements about NADPH-cytochrome P450 reductase.

Key concepts

Cytochrome P450 Enzymes

Cytochrome P450 enzymes are a vast and diverse family of proteins that play an essential role in the metabolism of a wide variety of substances. These enzymes are responsible for the detoxification of xenobiotics, drugs, and environmental contaminants, as well as the synthesis of important biological molecules like steroids and lipid-soluble vitamins.

Each cytochrome P450 enzyme contains a heme prosthetic group that gives it its characteristic absorption spectrum, often seen as a peak at around 450 nm when reduced and bound to carbon monoxide. The electron transfer that takes place during their catalytic cycle is crucial for the conversion of substrates through oxidation reactions. Cytochrome P450 enzymes collaborate with partners like NADPH-cytochrome P450 reductase to receive the electrons necessary for these reactions.

Electron Transfer

Electron transfer is a fundamental concept in cellular metabolism and biochemistry. It's the movement of electrons from one molecule to another during chemical reactions, particularly reduction-oxidation (redox) reactions. In the context of cytochrome P450 reactions, electron transfer is facilitated by NADPH-cytochrome P450 reductase.

In this process, the reductase acts as an intermediary, initially receiving electrons from NADPH and subsequently shuttling them to the cytochrome P450. This transfer is made possible through the prosthetic groups FAD and FMN, which undergo reversible redox changes carrying electrons from the NADPH to the cytochrome enzyme.

Flavoproteins

Flavoproteins are a class of proteins that incorporate flavin molecules—FAD (flavin adenine dinucleotide) or FMN (flavin mononucleotide)—which serve as prosthetic groups. These proteins perform various functions, including supporting the process of cellular respiration, photosynthesis, DNA repair, and growth. They are critical in electron transport chains due to their ability to participate in one- or two-electron transfer processes.

NADPH-cytochrome P450 reductase qualifies as a flavoprotein because it contains both FAD and FMN. These flavin groups undergo oxidation-reduction reactions, enabling the transfer of electrons from NADPH to the cytochrome P450 enzymes during the detoxification or synthesis of biomolecules.

Prosthetic Groups

Prosthetic groups are non-protein molecules that bind tightly, often covalently, to proteins, allowing those proteins to function effectively. They are essential for the biological activity of the proteins they are associated with. Prosthetic groups include a variety of different molecules, such as metals, vitamins, and other organic compounds.

In a specific reference to NADPH-cytochrome P450 reductase, the flavin moieties FAD and FMN serve as prosthetic groups. Their role is vital in capturing and transferring electrons. This means that not all prosthetic groups are the same; they differ based on the requirements of the protein they are part of and play diverse roles in the myriad of biological processes.