Problem Set 2

 

2)                  Describe the effects of the following on the p50 of Hb:

a.      Increase pH from 7.2 to 7.5

 

b.      Increase pCO2 from 20 mm t 40 mm:

 

c.       Dissociation into monomers

 

3)                  Below is a set of data for oxygen binding by whole human blood:

 

pO2

%
Saturation

Q

0

0

0

10.6

10

0.1

19.5

30

0.3

27.4

50

0.5

37.5

70

0.7

50.4

85

0.85

77.3

96

0.96

92.3

98

0.98

 

a.      Plot the binding curve:

 

Now Estimate % saturation at:

100 mm Hg:

 30 mm Hg:

b.      What percent of bound O2 is delivered to the tissues?

 

 

c.       Assume pH = 7.6 in the lungs and 7.2 in the tissues.   See Figure 5-16 in Lehninger.

Per the figure, q at 30 mm Hg, pH 7.2 is ~ 35% (or so – picture isn’t that good…)

Now, what percent of bound O2 is delivered?

 

 

7)                  Data for oxygen binding by Callianassa (ghost shrimp of Texas beaches, actually) is shown below( with the Hill Plot):

 

pO2

Q

1.1

0.003

7.7

0.019

10.7

0.035

31.7

0.084

71.9

0.19

100.5

0.329

123.3

0.487

136.7

0.557

166.8

0.673

203.2

0.734

262.2

0.794

327

0.834

452

0.875

736.7

0.913

 

      Draw the Hill plot and tell me:        

a.      P50 

b.      nH

c.       Minimum number of subunits:

 

 

10)              Some (not many) proteins exhibit negative Cooperativity:

d.      What would a Hill plot look like for negative cooperativity?

b.      Would either of the models for cooperativity we talked about (Monod vs. Koshland) allow for negative cooperativity?

 

 

11)              A biochemist with time on his hands constructs a mutant hemoglobin where the proximal histidine (His F8) is replaced with glycine and the heme bound to a free imidazole ring:  Cooperativity is reduced (no surprise there, since there is no motion of the F helix upon O2 binding).  However, the O2 affinity is also increased.  Why?

 

12)              The following is an imaginary O2 binding protein.  Residue 13 in each monomer is a histidine; residue 85 is an aspartic acid.  O2 binds in between the two Fe’s attached to Helix A and Helix C of each monomer..:

scan

a.      Is the molecule likely to be cooperative?

 

 

b.      Does the molecule show a Bohr Effect?

 

 

c.       What would be the effect of replacing Asp85 with Lysine.?

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