Download Lehninger Chapter 5, Part 1

David L. Nelson and Michael M. Cox
Lehninger Principles of
Biochemistry
Fourth Edition
Chapter 5:
Protein Function
Copyright © 2004 by W. H. Freeman & Company
Invariant Amino Acids
Position
Amino Acid
Function
F8
His
Proximal, links to heme
E7
His
Distal, heme contact
CD1
Phe
Hydrophobic heme contact
F4
Leu
Hydrophobic heme contact
B6
Gly
Allows close approach of B and E helices
C2
Pro
Helix termination
HC2
Tyr
Links H and F helices
C4
Thr
Uncertain
H10
Lys
Uncertain
Myoglobin/hemoglobin subunit
Figure 5-3
1
Porphryin Ring
pyrrole ring
planar
Figure 5-1a
Figure 5-1
Fe in +2
6 coordination sites
Protoporphyrin IX
4 N of porphyrin
Vinyl, methyl, and
proprionyl groups
his F8 of protein
(proximal)
molecular oxygen
Figure 5-1b
Figure 5-1c
2
Figure 5-6
Hydrophobic in, proprionate out
Figure 5-20a
Role of the distal heme
Deoxyhemoglobin – form of hemoglobin with no O2 bound
dull red in color
Oxyhemoglobin – form of hemoglobin with 1 O2 at each heme
bright red
oxygenation not oxidation
Methemoglobin – iron is oxidized to Fe3+
brown
Carboxyhemoglobin – carbon monoxide is bound at the heme
CO binds 210 tighter than O2
Cyanomethemoglobin – cyanide is bound at the heme
binds to Fe3+
use to combat cyanide poisoning
draw from mitochondria
Why does the heme group need to be in a protein?
a) oxidation to Fe3+ - “heme” sandwich
b) damaging radicals
c) CO binds 200,000 times tighter to free heme
Figure 5-5a and b
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