Protein Function Flashcards
How many subunits in hemoglobin
four (oligomer)
Function of myoglobin?
Reserve of O2 during intense exercise
Where does the proximal histidine (His 93) bind to the heme group
5th coordinate position
How is the porphyrin ring held in place (with myoglobin)
Hydrophobic interactions AND coordination bond between Fe and proximal histidine (His F8)
Where does O2 bind to the heme group
6th coordinate position of Fe
Which histidine assists in O2 binding to heme
Distal histidine (His E7/64)
What is the point of heme being attached to globin
Increases specificity and affinity for O2, CO binds with less affinity
What kind of plot is used to represent O2 binding to myoglobin
Hyperbolic plot
What kind of subunits does Hemoglobin have
Two alpha and two beta chains
How are myoglobin, beta-globin and alpha-globin similar?
Each have 8 alpha helices with heme binding pockets, they bind O2 in the same manner as myoglobin
What kind of affinity is indicated by a hyperbolic curve
Constant (monomers)
Function of myoglobin vs hemoglobin
Mb: transport/store O2 within tissue
Hb: transport O2 from lungs to tissue
What is hemoglobin tense state?
Low affinity for O2 (deoxy Hb, large central cavity)
What is homoallostery
Binding of effector affects further binding of same compound (usually ligand increases its own affinity; sigmoidal curve)
What is heteroallostery
Binding of effector affects further binding of different compound (either activators or inhibitors)
When is the iron atom lowered from the heme groups plane?
In the T state (with no O2 bound)
What happens when O2 binds
Fe moves into plane, His F8 moves with it. O2 binding site becomes high affinity (O2 binds more readily to R state)
Which Hb effectors are negative effects on O2 binding
H+, CO2 and BPG favour the T state (O2 favours R state)
What does 2,3-bisphosphoglycerate do in Hb
Stabilizes the T state
What does CO2 do as an allosteric effector
Acts directly and indirectly to stabilize the T state (favours T state)
What does H+ do in Hb
Lowers pH therefore protonates side chains (His–>His+, NH2–> NH3+). Once His is protonated this enhances BPG binding and reduces O2 binding
BOHR EFFECT
When is the R state favoured
At high pp O2 and relatively high pH
When is the T state favoured
At high [H+] and high CO2 and low pp O2
What are the roles of His residues in Hb
His F8 (prox) = attachment of heme His E7 (distal) = assist O2 binding, decrease affinity of CO 4 His in central cavity = BPG binding
