1.09 Flashcards
(27 cards)
Ligand
That which is tied. Denotes a compound that can bind to a protein.
Define allosteric
Other form. Denotes more than one conformational state of a protein.
Logan’s-binding group
The group on the protein that engages the ligand
T state
Tight or taut. A conformational state showing weak binding of O2.
R state
Relaxed. A conformational state showing strong binding of O2.
Ligand binding is these 3 characteristics
Non catalytic
Often causes a protein conformational change
can be regulatory
The fractional percent of ligand binding sites occupied can be represented by this equation
of binding sites occupied/ total # of binding sites in solution
[PL]/[P]+[PL]
Dissociation equilibrium equation can be written as:
[PL]=[P][L]/Kd
What does it mean when [L]=Kd ?
50% of the ligand binding sites are occupied
What is Kd also Known as?
P50
What is Kd equivalent to?
To the molar concentration of the ligand at which half the ligand binding sites are occupied
If the Kd is lower, is the affinity of protein higher or lower?
The affinity is higher of the ligand to the protein
If the concentration of the ligand required for 50% is lower of the binding sites to be occupied, is the protein more tightly bound or loosely bound to the ligand?
The protein is more tightly bound to the ligand
What is myoglobin’s fiction?
Oxygen storage and transport protein in muscles
What is hemoglobin’s function?
An identical capacity in blood vessels (oxygen storage and transport protein in blood vessels)
What kind of fold are myoglobin and hemoglobin built on?
A common structural motif-global fold
What do the polypeptide chains of the hemoglobin and myoglobin fold around?
A prosthetic group- heme ( Fe(II) protoporphyrin IX)
O2 being not very soluble in aqueous solutions, what is used to transport O2?
Iron incorporated into a prosthetic group, heme
What are key factors to the oxygen binding to heme in Mb?
- 4 porphyrin an atoms coordinate Fe (II)
- one N from His F8 (His 93- 8th red l the F helix)
- His E7 hydrogen bonds to O2 (His 64- 7th res of E helix)
- bounded O2 acts as the 6th ligand to the Fe (II)
What color does blood change to when O2 binds to the Fe (II) heme complex altering the electronic state of the complex causing a change in color?
Blood goes from dark purple venous blood to scarlet arterial blood
What does the oxidation of the Fe (II) to Fe (III) prevent?
Prevents the binding of O2
What is Fe (III) also known as and what color is it?
Also known as met myoglobin and the complex is colored brown
What other compounds can bind to the Fe (II) heme complex? Why are they toxic?
CO, NO, H2S. Their binding affinity is higher than that of O2 therefore toxic.
Why is the Kd for CO 200x smaller than the Kd of O2 for Mb bound Heme?
Because of steric interference with the distal His, His E7. Sterics help to favor O2 binding.
