protein structure and function of Mb and Hb

what type of metabolism did ancient organisms use

anaerobic metabolism

what concentration of oxygen can hemoglobin carry

0.01 M

what is myoglobin

an intracellular protein found in muscle tissue

what is myoglobin’s function

to facilitate oxygen transport in respiring muscle tissue

why is the rate of oxygen delivery limited in the capillaries

low solubility of oxygen in aqueous solution

what increases solubility of oxygen in muscle tissue

myoglobin

what is myoglobin composed of

a single polypeptide chain of 153 residues in 8 alpha helices

in protoporphyrin what state is the central iron in

FeII ferrous state

if iron oxidizes into ferric what does it become

metmyoglobin or methemoglobin

what happens when the met forms bind oxygen

the heme coordinates tightly to a watermolecule as sixth ligand

what does methemoglobin do

converts FeIII to FeII

free heme in solution readily binds to oxygen but what happens shortly after

oxygen oxides to ferrous state

iron atoms in heme prefer to bind six ligands in what type of geometry

octahedral

what are four ligands of the heme

nitrogen atoms of 4 oyrrole rings

where does the 5th ligand in heme come from

histadine F8

what is the 6th ligand in heme

oxygen binding to ferrous heme

what becomes the 6th ligand for a heme in the ferric state

water

in the deoxygenated state how is heme coordinated

by the 4 nitrogens of the pyrroles and nitrogen of histadine

when oxygen binds where does it bind on the heme and why

opposite face of the heme from histadine so the FeII center is octahedrally coordinate

what happens upon oxygenation

the electronic state of the heme changes but iron remains in ferrous state

what is the oxygenated heme of myoglobin called

oxymyoglobin

what angle is the oxygen atom bound to the heme

60 degree, not perpendicular

what is the unoxygenated heme of myoglobin called

deoxymyoglobin

what is in the 6th coordination site of deoxymyoglobin

nothing it is vacant

what is on the same side of the heme that oxygen binds to

His E7

why is the oxygen binding site sterically hindered

His E7 is too far away to coordinate with the iron of the heme but it can sterically interact with the binding of oxygen

the free heme in solution has a high affinity for what

carbon monoxide

why does CO bind greater in Mb and Hb

His E7 forces the CO molecule to tilt away from the preferred perpendicular alignment of the plane of the heme

what happens because of the reduced affinity of Mb/Hb for CO

trace amounts of CO can be generated during metabolism which would otherwise occupy Mb/Hb sites

how many ligands and angstroms is the ferrous iron atom in deoxymyoglobin

5 ligands and 0.55 angstroms above the plane towards His F8

what happens to the iron porphyrin complex in deoxymyoglobin

it gets a dome shape

what happens when oxygen binds

the iron atom is pulled back into plane of the heme so it is 0.26 angstroms above porphyrin

what is the hill coefficient for myoglobin

1

what does a hill coefficient of 1 mean

oxygen atoms bind independently of each other

what is the partial pressure of oxygen in arterial blood

100 torr

what is the partial pressure of venous blood

30 torr

what is the P50 of the Mb oxygen binding curve

2.8 torr

myoglobin binds under what conditions compared to hemoglobin

the same conditions as hemoglobin releasing it

if n=1

myoglobin and non cooperative binding

if n>1

positively cooperative, ligand binding increases affinity of protein for more ligand binding

if n<1

negatively cooperative, ligand binding decreases affinity of protein for more ligand binding

what is 1-Ys

fraction of unbound sites

what is monomeric

myoglobin

what is tetrameric

hemoglobin

what is a heme

a porphyrin ring coordinated to an iron atom

how can heme bind oxygen

the iron must be in the ferrous state

what happens to iron in the ferric state

iron binds water very tightly

iron in ferrous state

Fe²⁺

iron in ferric state

Fe³⁺

why is hemoglobin significant

must be able to bind oxygen in the lungs and release oxygen in the capillaries

what enzyme converts a ferric iron to the ferrous state

methemoglobin reductase