Question

Glutathione does all of the following except A. participate in the transport of amino acids across some cell membranes. B. scavenge peroxides. C. form conjugates with some drugs to increase water solubility. D. decreases the stability of erythrocyte membranes. E. acts as a cofactor for some enzymes.

Short answer

Glutathione does NOT perform the function of decreasing the stability of erythrocyte membranes. Instead, it helps maintain the stability and integrity of these membranes, preventing hemolysis (rupture of red blood cells).

Step-by-step solution

Option A: Participate in the transport of amino acids across some cell membranes

Glutathione is known to be involved in the transport of certain amino acids across cell membranes. Therefore, this option is not the correct one since Glutathione performs this function.

Option B: Scavenge peroxides

Glutathione acts as an antioxidant, which means it can scavenge and neutralize reactive oxygen species, such as peroxides, in cells. Thus, this option is also incorrect because Glutathione performs this function.

Option C: Form conjugates with some drugs to increase water solubility

Glutathione plays a role in the detoxification of xenobiotics (foreign substances) in cells, including drugs. One of the ways it does this is by forming conjugates with some drugs to increase their water solubility and facilitate their removal from the body. This option is incorrect since Glutathione performs this function.

Option D: Decreases the stability of erythrocyte membranes

Stability of erythrocyte (red blood cell) membranes is important for proper cellular function. Glutathione actually helps maintain the stability and integrity of erythrocyte membranes, thereby preventing hemolysis (rupture of red blood cells). Therefore, this is the correct answer because Glutathione does NOT decrease the stability of erythrocyte membranes; instead, it plays a role in maintaining it.

Option E: Acts as a cofactor for some enzymes

Glutathione serves as a cofactor for certain enzymes, such as glutathione peroxidase and glutathione-S-transferase. These enzymes play critical roles in detoxification and antioxidant defense systems in cells. This option is incorrect because Glutathione indeed performs this function. So, based on the analysis of each option, the correct answer is: D. decreases the stability of erythrocyte membranes.

Key concepts

Antioxidant Mechanism

Glutathione, a small peptide found in our cells, is widely known for its role in protecting the body from oxidative stress. One of its fundamental functions is as an antioxidant. This means glutathione effectively neutralizes harmful molecules called reactive oxygen species (ROS), which include peroxides. These harmful molecules can cause significant damage if left unchecked, leading to cellular damage and playing a role in various diseases, such as cancer and heart disease.

The antioxidant mechanism of glutathione involves the thiol group in its cysteine residue, which is highly reactive. Through a process known as redox reaction, glutathione donates an electron to the unstable ROS, thereby stabilizing them and rendering them harmless. This action helps in preventing cellular damage that could lead to premature aging and chronic diseases. Moreover, glutathione recycles other antioxidants, such as vitamin C and E, back to their active forms, bolstering the body's overall defense mechanisms.

Erythrocyte Membrane Stability

Another crucial role of glutathione pertains to the stability of erythrocyte membranes. Erythrocytes, commonly known as red blood cells, transport oxygen throughout our bodies. The membrane of these cells must remain intact and flexible to navigate through the narrowest blood vessels. Glutathione contributes to this membrane stability by directly protecting it from oxidative damage and by ensuring proper protein and lipid function within the membrane.

When glutathione levels are sufficient, it preserves the integrity and deformability of erythrocytes, enabling them to withstand the mechanical stress they encounter in circulation. A deficiency in glutathione can lead to the weakening of the erythrocyte membrane, which may cause premature rupture or hemolysis, with severe implications for oxygen transport and delivery. Hence, maintaining optimal glutathione levels is crucial for the resilience and proper function of our red blood cells.

Xenobiotic Detoxification

The body is continually exposed to various foreign compounds, which are collectively termed xenobiotics. These substances can be drugs, pollutants, or even food additives—introducing potential toxins into our systems. Glutathione plays a vital role in the detoxification process of these xenobiotics by transforming them into forms that are more easily excreted.

Conjugation Reaction

One of the primary ways in which it does this is through conjugation reactions. Glutathione attaches itself to the lipid-soluble xenobiotics, making them more water-soluble. This reaction is facilitated by enzymes known as glutathione-S-transferases (GSTs).

Subsequent Elimination

Once conjugated, these transformed xenobiotics are then excreted via the urine or bile. This process is crucial for the protection against potential toxicity that can result from the accumulation of xenobiotics in the body. It is also a fundamental mechanism by which the body can tolerate and eliminate prescription drugs and environmental chemicals safely.