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February 10 th and 12 th , 2010 Biochemistry Recitation MBioS 303 - - PDF document
February 10 th and 12 th , 2010 Biochemistry Recitation MBioS 303 - - PDF document
2/10/2010 February 10 th and 12 th , 2010 Biochemistry Recitation MBioS 303 Spring 2010 Review: Beta Sheets 1 2/10/2010 Review: Beta Sheets QUIZ 2 2/10/2010 Todays Topics Myoglobin and Hemoglobin! Myoglobin Versus Hemoglobin
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Today’s Topics
Myoglobin and Hemoglobin!
Myoglobin Versus Hemoglobin
MYOGLOBIN:
One polypeptide 8 -helices (A-H) Heme group – how many? Extremely compact protein
structure
Oxygen STORAGE in muscle
Must be able to bind O2, then
release where and when needed
HEMOGLOBIN:
Four polypeptides 8 -helices (A-H) Heme group – how many? Extremely compact protein
structure WITHIN SUBUNITS
Oxygen TRANSPORT from
lungs to tissue
Must be able to bind O2, then
release where and when needed
Each human red blood cell is 95% hemoglobin (dry weight), which is about 270,000,000 hemoglobin molecules
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Myoglobin and Hemoglobin Myoglobin and Hemoglobin
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Heme Group
What molecule(s) bind to the iron atom in heme?
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Allostery and Cooperativity
Allostery: binding of a
ligand at one site effects binding of ligand at another site
Cooperativity: special
case of allostery in which affinity for ligand changes with amount of ligand already added
Characteristic sigmoidal
curve
Hemoglobin: T to R Transition
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What Initiates T to R State Change? Hemoglobin: T to R Transition
!
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Hemoglobin: T to R Transition
!
Stabilization of R and T States
T STATE:
Hydrogen bonds Salt bridges H+ CO2 2,3-BPG
R STATE: O2 CO
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Hemoglobin: O2 binding
1st O2 that binds binds
weakly
T to R transition Increased affinity
(cooperativity!)
Hemoglobin: H+ and CO2 binding
Binding of H+ and CO2
inversely related to O2 binding
pH of blood = 7.6 in lungs,
7.2 in tissues
H+ binds amino acids,
stabilizing T state
CO2 binds as carbamate to
N-terminal amino group, forming additional salt bridges that stabilize T state
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Hemoglobin: 2,3-BPG binding
Binds in pocket between
β subunits
Stabilizes T state Important for
adaptation at high altitudes
Hemoglobin: CO binding
Binds to iron in heme
group – competes with O2!
Stabilizes R state
(prevents release of O2 back into tissues)
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