1. BPG binds to hemoglobin and thereby affects hemoglobin’s ability to bind oxygen.
   1. Each beta subunit contributes 3 residues that bind BPG: His2, Lys82, and His143. How is it possible for all three of these residues, distant in the amino acid sequence, to bind BPG?
2. 
   
   1. BPG and His143 interact in Hemoglobin’s central cavity. What’s the strongest type of interaction possible between His and BPG: ________________ and between HHis⁺ and BPG:________________. Which of these BPG interactions (with His or HHis⁺) is stronger?
3. 
   
   1. If His143 has the standard pKa for a free Histidine (see table on page 1), what is the probability that His143 will be protonated at blood pH of 7.4? Show your work for full credit.
4. 
   
   1. What His143 pKa value would give ≥90% of His143 in the protonated state at pH 7.4? Justify your answer/show your work.