Structure to Function - Myoglobin and Hemoglobin

What is the effect of oxygenation on myoglobin?

alters electronic state of Fe (2) → hemoglobin turns from purple to scarlet red

What is the effect of oxidation on myoglobin?

oxidated Fe (1) to Fe (2) → met-hemoglobin and met-myoglobin turn brown

What other molecules bind to heme groups, have higher affinity than O₂, and are more toxic?

carbon monoxide (CO), hydrogen sulfide (H₂S), and nitric oxide (NO)

In myoglobin, how does O₂ bind?

the heme group (organic ring holding the Fe²⁺) prevents oxidation and allows O₂ to bind reversibly

ligand

molecule that binds to a protein

binding site

where the ligand binds, complementary to ligands in:

• shape

• size

• charge

• hydrophobic/hydrophilic characters (water-fearing vs. water-loving characters)

how does protein str impact func?

1) reversible, specific molecular interactions

2) structural flexibility (meaning undergo subtle or dramatic shape changes (conformations)

electrostatic interactions contribute to protein stability

van der Waals, H-bonds, and ion pairs / salt bridge

What is the T state?

letting go of O₂ (unliganded) > low O₂ affinity > deoxyHb

What is R state?

receiving the O₂ (liganded) > high O₂ affinity > oxyHb

cooperative binding

binding of a ligand to 1 site affects the binding site of additional ligands to other sites

What is the effect of O₂ on hemoglobin?

1) each O₂ binding to a subunit increases the O₂ affinity of the remaining subunits

a) 4th O₂ binds to a Hb w 100-fold greater affinity than the first O₂

When T transitions to R, what is happening in terms of the movement of the heme and F helix?

from the T to R transition, the O₂ binds to the Fe (2) of the heme group → pulls the histidine and then the helix F downwards