Question

. Studies have found that aromatase activity is high in obese individuals, yet in animal models, those lacking aromatase are obese. What is the best explanation for this? A. At high concentrations of fat tissue, the aromatase reaction rate increases past the Vmax in a nonobese individual. B. The reaction’s product serves to inhibit aromatase when it is present at high levels. C. The enzyme requires a higher activation energy to successfully complete the reaction in the obese individual. D. The enzyme structure changes in obese individuals, and the wrong substrate is being catalyzed by the reaction.

Short answer

The product of the aromatase reaction inhibits aromatase when present at high levels (Option B).

Step-by-step solution

Understand the Problem

The problem describes a paradox where aromatase activity is high in obese individuals but, paradoxically, animals lacking aromatase are also obese. We need to find the best explanation for this contradictory observation.

Evaluate Option A

Option A states that the aromatase reaction rate increases past the Vmax in a non-obese individual. However, increasing past Vmax is not possible because Vmax is the maximum rate of the reaction when the enzyme is saturated with substrate.

Evaluate Option B

Option B suggests that the reaction’s product inhibits aromatase when present at high levels. This option is plausible since high levels of product could provide a feedback mechanism to inhibit further enzyme activity. This would explain high initial aromatase activity in obese individuals leading to product accumulation, which then inhibits aromatase.

Evaluate Option C

Option C implies the enzyme requires higher activation energy in obese individuals. However, there is no evidence provided that supports a change in activation energy required for the reaction based on obesity.

Evaluate Option D

Option D suggests a change in enzyme structure leading to the wrong substrate being catalyzed. There is no information indicating a structural change in aromatase in obese individuals that affects substrate specificity.

Determine the Best Explanation

Based on the evaluation of options, Option B offers the most plausible explanation. The product of the aromatase reaction potentially inhibits the enzyme when present in high concentration, explaining why animals lacking aromatase (hence lacking the product) are obese, while the product builds up in humans and reduces further aromatase activity.

Key concepts

Aromatase and its Role in Obesity

Aromatase is an enzyme that converts androgens into estrogens. This process is crucial as it balances hormone levels in the body. Interestingly, its activity has been linked to obesity.
Studies show that obese individuals have high aromatase activity. However, animals that lack aromatase are also obese. This seems paradoxical at first glance.
This paradox can be explained by feedback inhibition. In obese people, the product of the aromatase reaction might build up and inhibit further activity, leading to complex patterns in hormone levels.

Feedback Inhibition

Feedback inhibition is a regulatory mechanism where the end product of a reaction inhibits the enzyme that produces it. This is a way for the body to maintain balance and prevent the overproduction of certain substances.
In the case of aromatase, high levels of its reaction product (estrogens) could inhibit further activity of the enzyme. This means that after a certain point, more product stops the enzyme from working as much, balancing the levels of the product.

• Maintains balance within biological systems
• Prevents overproduction of substances
• Critical for maintaining hormone equilibrium

The inhibition of aromatase through its product can explain why high activity is seen in obesity but leads to a stop when product levels are sufficient.

Enzyme Kinetics and Vmax

Enzyme kinetics is the study of how enzymes bind to substrates and convert them to products. A key concept here is the enzyme’s maximum reaction rate, or Vmax.
Vmax represents the fastest rate at which an enzyme can catalyze a reaction when fully saturated with its substrate.
Importantly, an enzyme working at its Vmax cannot go any faster regardless of substrate concentration. This makes it clear that the hypothesis stating the rate will surpass Vmax in obese individuals is incorrect.

• Essential concepts: reaction rate, enzyme saturation
• Vmax: maximum catalytic activity
• Irrelevance of substrate concentration once Vmax is reached

Obesity and Enzyme Activity

Obesity is characterized by excessive fat accumulation. This condition impacts various metabolic pathways and enzyme activities.
Enzyme activities can change due to different factors like altered expression levels, increased substrate availability, or through feedback mechanisms. In the case of obesity, these changes could contribute to a complex biological scenario where enzyme activity, like that of aromatase, is initially high but regulated down by its products.

• Alters metabolic pathways
• Influences enzyme regulation
• Feedback inhibition plays a role

This explains why both high aromatase activity and its absence could be linked to obesity in different contexts.