Use the following information to answer questions: Indoleamine 2,3-dioxygenase (IDO) 1 catalyzes the first and rate-limiting step of L-tryptophan degradation in the tryptophan-kynurenine pathway. The direct product of IDO1 is N´-formylkynurenine, which breaks down non-enzymatically to L-kynurenine by losing its formyl group. His-tagged human IDO1 cDNA was expressed in Escherichia coli and purified using a nickel column. IDO1 activity was measured in the absence and presence of various potential inhibitors in buffer at pH 6.5. Galanal was found to inhibit IDO1 activity, and based on the... Show more

Use the following information to answer questions:

Indoleamine 2,3-dioxygenase (IDO) 1 catalyzes the first and rate-limiting step of L-tryptophan degradation in the tryptophan-kynurenine pathway. The direct product of IDO1 is N´-formylkynurenine, which breaks down non-enzymatically to L-kynurenine by losing its formyl group. His-tagged human IDO1 cDNA was expressed in Escherichia coli and purified using a nickel column. IDO1 activity was measured in the absence and presence of various potential inhibitors in buffer at pH 6.5. Galanal was found to inhibit IDO1 activity, and based on the Michaelis-Menten kinetics of IDO1, its inhibitory mode was further studied by measuring the initial rate of L-kynurenine production in the presence and absence of 30 µM galanal at various L-tryptophan concentrations (Figure 1).

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MCAT Chemical and Physical Foundations of Biological Systems 17

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5 Questions

1. The following table provides pKa values for four buffers at room temperature:

Which buffer would be most appropriate for measuring IPO1 reactivity?

Potassium phosphateTEATrisPotassium acetate

2. The following table provides pKa values for four buffers at room temperature:

Which buffer would be most appropriate for measuring IPO1 reactivity?

TrisTEAPotassium acetatePotassium phosphate

3. The mode of IDO1 protein purification described in the passage is an example of

anion exchange chromatography.affinity chromatography.cation exchange chromatography.size exclusion chromatography.

4. Based on the described enzymatic activity of IDO1, what is the structure of L-kynurenine?

ABDC

5. The mode of IDO1 protein purification described in the passage is an example of

cation exchange chromatography.affinity chromatography.anion exchange chromatography.size exclusion chromatography.