Bioc405 L7

Front 1

Myoglobin basic structure

Back 1

-Contains a spherical red heme group in the center of Fe(II)

- made up of eight helices

Front 2

Oxo-myoglobin Fe(II) group bonds

Back 2

- Bound to the four Nitrogen of the heme group

- One molecule of O2 can bind

- Also bound to His F8

Front 3

The Myoglobin heme complex structure

Back 3

The heme group is packed between hydrophobic side chains of Val E11 and Phe CD1

** when O2 is bound to the Fe(II), it also interacts with the NE2 of the imidazole of HisE7

Front 4

What is YO2?

Back 4

Stands for the fractional oxygen saturation: the amount of O2 bonding sites occupied by oxygen

Mathematically:

Y = pO2 / (pO2 + K), where K = [ O2][Mb]/[MbO2]

Front 5

P50

Back 5

The partial pressure of O2 (pO2) when saturation (Y) =0.5

**pO2 in venous blood is about 30 torr. 760 torr =1atm

Front 6

Myoglobin O2 binding curve

Back 6

The shape of the curve is hyperbolic

Front 7

Hemoglobin general information

Back 7

The oxygen transporter in the blood of most animals, usually embedded in RBC's

- consists of four myoglobin-like subunits

- two Hb chains are called a chains, which have the same amino acid sequence

- there are also two B chains that have the same sequence

Front 8

"Cooperativity" in hemoglobin

Back 8

Refers to the cross-talk between the four subunits of hemoglobin

-increases the efficiency of O2 transport from lungs to other organs

- responsible for the sigmoidal binding curve

Front 9

Deoxy versus Oxo Hemoglobin

Back 9

Deoxy Hb = T state

Oxy Hb = R state

- in oxy state, the central site gets smaller

- salt bridges in the T state are broken in the R state

Front 10

O2 binding to heme in Hemoglobin

Back 10

1. Fe move into the plane of heme, which becomes planar when the O2 binds

2. NO oxidation or reduction of Fe(II) occurs

3. Movement of His F8 acts like a trigger

4. Protons released due to change in pKa of groups in salt bridges

Front 11

Changes in the heme groups upon oxygenation: "the trigger"

Back 11

Upon oxygenation: the movement of the Fe2+ into the plane of the heme group,and the greater planarity of the heme after this move, is the “trigger” of the T-state (Deoxy-Hb) to R-state (Oxy-Hb) transition

Front 12

Deoxy versus Oxy Hemoglobin absorbance

Back 12

As more O2 binds, the visible spectrum shifts from blue to red.

At 580nm, you can measure how much has been oxygenated

Front 13

O2 binding in Hemoglobin versus Myoglobin

Back 13

Hb picks up O2 in lung and delivers to tissue much more efficiently.

- Hb is much less saturated (has more room for O2 to bind) than Mb at venous pO2

Front 14

The Hill Equation

Back 14

The equation used to describe the sigmoidal curve of Hb-O2 binding. The larger the Hill coefficient, the steeper the S-shaped O2 binding plot.

Front 15

The Bohr Effect

Back 15

Describes the delivery of O2 from a region of higher pH (the lungs) to lower pH (the tissue)

Front 16

The Allosteric Effect

Back 16

The binding of one ligand at one site affects the binding ofanother ligand at another site. This often, but not necessarily always, requires interactionsbetween subunits of oligomeric proteins.

Front 17

The Symmetric model of allosteric proteins

Back 17

Assumes that each subunit can exist in either T or R. and the the ligand can bond to either conformation

** The key point is that hemoglobin cannot adopt an intermediate conformation.The tetramer is either in the deoxy (T) state or in the oxy (R) state.

Front 18

The Sequential Model of allosteric proteins

Back 18

Main difference is that it assumes that symmetry does not need to be maintained and that subunits can adopt multiple conformations

Front 19

BGP (D-2,3-Bisphosphoglycerate): what it is and where it binds

Back 19

At high altitude the [BGP] in blood increases from ~4mM to ~8mM

- binds at the central cavity between the B-chains in deoxy Hb. Does NOT bind to Oxy Hb

Front 20

Effects of BPG

Back 20

The net effect of BGP is to decrease Hb's affinity for O2, which increases the efficiency of O2 delivery significantly

How?: increase in [BPG] causes the P50 of Hb to increase from 26 to 31 torr.

Front 21

Hemocyanin

Back 21

The oxygen binding protein in blue blood of mollusks and arthropods

- much larger than hemoglobin

-O2 binding site is based on Cu, not Fe(II)

Mollusk hemocyanin: gigantic cylinders with 10-20 subunits per cylinder

Arthropod hemocyanin: hexameters with D3 dihedral symmetry (6 subunits/hexamer)

Front 22

O2 binding center in hemocyanin (v general)

Back 22

Oxygen (red) bound using two Cu(I) ions (purple) liganded by six histidines.And all embedded in a totally different protein environment than in hemoglobin.

Front 23

Sickle Cell Anemia

Back 23

Makes RBC's rigid and jagged, making it extremely challenging to pass through capillaries

- The prime event is the point mutation fromGlu6 in HbA to Val6 in the HbS β-chain.

-Heterozygotes with 40% HbS still have normal RBCs.

- Common in South Africa because it confers immunity to Malaria

Front 24

B1 to B2 mutation in Sickle Cell Anemia

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Deoxy HbS tetramers start to form fibers in an uncontrolled manner. Under deoxy conditions, these RBCs cannot pass trough capillaries

Front 25

Myoglobin and Hemoglobin differences: (subunits and hemes bonded)

Back 25

Hemoglobin has four subunits and bond 4 heme groups

Myoglobin has one subunit and binds one heme group