Question

The following enzymes of the kynurenine pathway are induced by pro- inflammatory cytokines such as IFN-g and TNF-a: a. tryptophan 2,3 dioxygenase, indoleamine 2,3-dioxygenase, kynurenine monoxygenase b. indoleamine 2,3-dioxygenase, kynurenine hydroxylase (monoxygenase), kynurenine aminotransferase c. indoleamine 2,3-dioxygenase, kynurenine hydroxylase (monoxygenase) d. tryptophan 2,3 dioxygenase, kynurenine hydroxylase (monoxygenase) e. only indoleamine 2,3-dioxygenase

Short answer

Answer: indoleamine 2,3 -dioxygenase, kynurenine hydroxylase (monoxygenase), kynurenine aminotransferase

Step-by-step solution

1. Analyzing Choice a

In choice a, the enzymes are tryptophan 2,3 dioxygenase, indoleamine 2,3 -dioxygenase, and kynurenine monoxygenase. Both tryptophan 2,3 dioxygenase and indoleamine 2,3-dioxygenase are the enzymes involved in the first step of the kynurenine pathway (converting tryptophan to N-formylkynurenine), but tryptophan 2,3 dioxygenase is regulated by the availability of tryptophan and is not induced by pro-inflammatory cytokines. Kynurenine monoxygenase is another enzyme involved in the kynurenine pathway. However, this choice is incorrect since it includes tryptophan 2,3 dioxygenase.

2. Analyzing Choice b

In choice b, the enzymes are indoleamine 2,3 -dioxygenase, kynurenine hydroxylase (monoxygenase), and kynurenine aminotransferase. Indoleamine 2,3-dioxygenase is induced by pro-inflammatory cytokines and is involved in the first step of the kynurenine pathway (converting tryptophan to N-formylkynurenine). Kynurenine hydroxylase (monoxygenase) is also known as kynurenine 3-monooxygenase, which is involved in the conversion of kynurenine to 3-hydroxykynurenine. Kynurenine aminotransferase participates in the synthesis of kynurenic acid from kynurenine. These enzymes are involved in the kynurenine pathway; therefore, this choice is correct.

3. Analyzing Choice c

In choice c, the enzymes are indoleamine 2,3 -dioxygenase and kynurenine hydroxylase (monoxygenase). Both of these enzymes are induced by pro-inflammatory cytokines and are involved in the kynurenine pathway. However, this choice is incomplete because it ignores kynurenine aminotransferase, which is an essential enzyme in the pathway.

4. Analyzing Choice d

In choice d, the enzymes are tryptophan 2,3 dioxygenase and kynurenine hydroxylase (monoxygenase). Tryptophan 2,3 dioxygenase is an enzyme involved in the first step of the kynurenine pathway, but it is not induced by pro-inflammatory cytokines, so this choice is incorrect.

5. Analyzing Choice e

Choice e states that only indoleamine 2,3 -dioxygenase is induced by pro-inflammatory cytokines. While it is true that this enzyme is induced by such cytokines, this choice is incorrect because there are other enzymes in the kynurenine pathway that are induced by IFN-g and TNF-a. Based on the analysis, the correct answer is: b. indoleamine 2,3 -dioxygenase, kynurenine hydroxylase (monoxygenase), kynurenine aminotransferase