5. A histidine residue (His146) in Hb subunit has a side chain pKa of 6.2 in the lung. Due to a conformational shift of Hb in the muscle, an amino acid moves into the close proximity of this histidine, shifting this His146 pka to 7.7: • a) what is the net charge of this His146 in the lung at pH 7.6 (show all the calculations)? • b) what is the net charge of this His146 in the muscle at pH 7.2 (show all the calculations)? • c) what is the likely identity of the residue that causes the pKa shift for His146 residue? Explain why such residue causes the shift in the histidine pka.

5. A histidine residue (His146) in Hb subunit has a side chain pKa of 6.2 in the lung. Due to a conformational shift of Hb in the muscle, an amino acid moves into the close proximity of this histidine, shifting this His146 pka to 7.7: • a) what is the net charge of this His146 in the lung at pH 7.6 (show all the calculations)? • b) what is the net charge of this His146 in the muscle at pH 7.2 (show all the calculations)? • c) what is the likely identity of the residue that causes the pKa shift for His146 residue? Explain why such residue causes the shift in the histidine pka.

Introduction to General, Organic and Biochemistry

11th Edition

ISBN:9781285869759

Author:Frederick A. Bettelheim, William H. Brown, Mary K. Campbell, Shawn O. Farrell, Omar Torres

Publisher:Frederick A. Bettelheim, William H. Brown, Mary K. Campbell, Shawn O. Farrell, Omar Torres

Chapter23: Enzymes

Section: Chapter Questions

Problem 23.75P

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The amino acid histidine has ionizable groups with pKa values of 1.8, 6.0, and 9.2, as shown. COOH H₂N-CH | CH ₂ pH = CH lonizable -COOH group COO- H₂N-CH 1.8 pk₁ CH2 H -COO- CH -HisH+ COO- H₂N-CH 1 6.0 pk2 CH ₂ H H N -His CH -NH COO- H₂N-CH 1 9.2 pk₂ CH2 -NH₂ H -N CH A biochemist makes up 80 mL of a 0.11 M solution of histidine at a pH of 5.1. She then adds 60 mL of 0.10 M HCl. What is the pH of the resulting solution?