HOMEWORK 5
BIOL/CHEM 5310
due Tuesday, October 8, 2002
Use graph paper or a computer for graphing problems (for spreadsheet see link).
1. VVP text , Chapter 7, page 194, problem 1, 3, 4, 5
2. The following data describe the binding of oxygen to human myoglobin at 37°C
| PO2 (torr) | Y | PO2 (torr) | Y | |
| 1 | .182 | 5 | .526 | |
| 2 | .308 | 8 | .64 | |
| 3 | .400 | 10 | .69 | |
| 4 | .471 | 15 | .77 | |
| 20 | .816 |
From these data make 2 plots: Y vs. PO2, and log(Y/1-Y) vs. log(PO2)
From the plots estimate P50. Which plot is more accurate for determining P50?
3. The following data represent oxygen binding by a non-hemoglobin protein:
| PO2 | Y | PO2 | Y | |
| .321 | .000478 | 15.04 | .666 | |
| .656 | .000999 | 18.08 | .814 | |
| 1.089 | .00199 | 21.24 | .884 | |
| 1.687 | .00397 | 26.74 | .938 | |
| 2.736 | .0099 | 37.77 | .970 | |
| 3.955 | .0245 | 58.5 | .988 | |
| 5.716 | .0594 | 90.6 | .994 | |
| 7.71 | .137 | 150 | .997 | |
| 9.71 | .262 | 293 | .998 | |
| 11.94 | .437 | 475 | .999 |
From these data make a Hill plot: log(Y/1-Y) vs. log(PO2)
Determine P50, nH, and the minimum number of oxygen binding sites in this protein.
4. The Bohr effect is described by the following equation:
Hb(O2)n Hx + O2 <=> Hb(O2)n+1 + xH+ (where x= 0.6 mol H+/mol O2 ) Assume pH=7.4
a) How many moles of H+ are released upon full oxygenation of one mole of Hemoglobin?
b) Assume that 30% come from a Histidine in the b subunit (beta) . How many moles of H+ is that, per mole of Hb? And how many moles per mole of b chain (beta)?
c) Assume this Histidine has a pKa of 8.0 in deoxyhemoglobin. What will be its pKa in oxyhemoglobin, if the pH is 7.4? (First calculate the fraction of protonated His in deoxyHb, at pKa=8.0. Then the answer in part b tells you what fraction is protonated in oxyHb.)