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Proteins that contain reduced Cys can react with oxygen from the air to form intra- or intermolecular disulfide bonds (Cys-Cys). To understand the role of air in Cys oxidation, we will analyze here how the amino acid Cys reacts with oxygen present in the air. The half-cell reactions for the formation of water and Cys-Cys are 4 H+ O2 +4 e 2 H₂O, &º= 0.816 V 2 H+ + Cys-Cys +2 e 2 Cys, º = -0.340 V a. Write the balanced net chemical equation for the electron transfer reaction for the

Proteins that contain reduced Cys can react with oxygen from the air to form intra- or intermolecular disulfide bonds (Cys-Cys). To understand the role of air in Cys oxidation, we will analyze here how the amino acid Cys reacts with oxygen present in the air. The half-cell reactions for the formation of water and Cys-Cys are 4 H+ O2 +4 e 2 H₂O, &º= 0.816 V 2 H+ + Cys-Cys +2 e 2 Cys, º = -0.340 V a. Write the balanced net chemical equation for the electron transfer reaction for the

Chemistry
Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
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**Proteins and Cysteine Oxidation:** Proteins that contain reduced cysteine (Cys) can react with oxygen from the air to form intra- or intermolecular disulfide bonds (Cys-Cys). To understand the role of air in Cys oxidation, we will analyze how the amino acid Cys reacts with the oxygen present in the air. The half-cell reactions for the formation of water and Cys-Cys are: 1. \( 4 \, \text{H}^+ + \text{O}_2 + 4 \, \text{e}^- \rightarrow 2 \, \text{H}_2\text{O}, \, \varepsilon^\circ = 0.816 \, \text{V} \) 2. \( 2 \, \text{H}^+ + \text{Cys-Cys} + 2 \, \text{e}^- \rightarrow 2 \, \text{Cys}, \, \varepsilon^\circ = -0.340 \, \text{V} \) **Tasks:** **a.** Write the balanced net chemical equation for the electron transfer reaction for the above half-cell reactions written in the direction that ultimately reduces \( \text{O}_2 \). **b.** What is the value of \( \varepsilon^\circ \) for the chemical reaction in part a? Be sure to include units. **c.** Calculate the value of the equilibrium constant at \( T = 25 \, °\text{C} \) for the reaction in part a. **d.** You prepare a 0.020 M solution of Cys at pH 7.0 and let it stand in contact with air at 25 °C. Estimate the concentration of (Cys-Cys) at equilibrium.
Transcribed Image Text:**Proteins and Cysteine Oxidation:** Proteins that contain reduced cysteine (Cys) can react with oxygen from the air to form intra- or intermolecular disulfide bonds (Cys-Cys). To understand the role of air in Cys oxidation, we will analyze how the amino acid Cys reacts with the oxygen present in the air. The half-cell reactions for the formation of water and Cys-Cys are: 1. \( 4 \, \text{H}^+ + \text{O}_2 + 4 \, \text{e}^- \rightarrow 2 \, \text{H}_2\text{O}, \, \varepsilon^\circ = 0.816 \, \text{V} \) 2. \( 2 \, \text{H}^+ + \text{Cys-Cys} + 2 \, \text{e}^- \rightarrow 2 \, \text{Cys}, \, \varepsilon^\circ = -0.340 \, \text{V} \) **Tasks:** **a.** Write the balanced net chemical equation for the electron transfer reaction for the above half-cell reactions written in the direction that ultimately reduces \( \text{O}_2 \). **b.** What is the value of \( \varepsilon^\circ \) for the chemical reaction in part a? Be sure to include units. **c.** Calculate the value of the equilibrium constant at \( T = 25 \, °\text{C} \) for the reaction in part a. **d.** You prepare a 0.020 M solution of Cys at pH 7.0 and let it stand in contact with air at 25 °C. Estimate the concentration of (Cys-Cys) at equilibrium.
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