Biochemistry: Myoglobin and Hemoglobin (Test 2)

β-Thalassemia

β globin is lost or cannot be expressed Homozygous: rely on gamma chains Heterozygous: one β gene is functional

Valine in Sickle cell does not want to be exposed to the aqueous environment (hydrophobic) therefore

it begins to clump

When oxygen binds to hemoglobin, it is hard to detect which model is happening because ____________ .

it happens so quickly

Allosteric Enzymes possess _________________

quaternary structure

BOHR effect is the

response of Hb to a change in pH and CO2

R form is stabilized by (4 things)

1. Binding of oxygen to Heme group 2. release of 2,3-BPG 3. Increase in pH 4. Decrease in CO2

Partial pressure of oxygen (pO2) in the lungs is

100 torr

Hemoglobin with __________ is going to release more oxygen

2,3-BPG

At biological pH, oxygen release is about ______ in tissues

66%

Sickle Cell Anemia happens because

A change from Glutamic Acid to Valine (going from a negative charge to a neutral charge) (Glutamic is hydrophilic, Valine is hydrophobic)

In order for beta chains to come together, there is __________

A change in the quaternary structure and some changes on the tertiary structure.

Binding of Iron (Fe2+) to oxygen causes what:

Histidine is pulled into ring plane and Histidine with helix shifts position, disrupting some ion pairs between subunits.

The iron ion lies slightly ________ the plane of the porphyrin in deoxyhemoglobin heme, but _________the plane of the heme on oxygenation.

Outside, Moves into

Transition from Deoxyhemoglobin (T state) to oxyhemoglobin (R state) occurs upon ________________ .

Oxygen Binding

High pH promotes

Oxygen binding (stabilizes R state)

Low pH promotes

Oxygen release (stabilizes T state)

______________ CANNOT accommodate 2,3-BPG

R state

It takes __________________ to saturate hemoglobin to 50% at ____________

higher pressure higher altitudes

In the gamma chains of Hb F, the _______ is replaced by _________

histidine serine

The binding of oxygen to myoglobin follows a _____________ curve

hyperbolic

As the oxygen begins to bind to the iron, the cavity itself begins to ___________

shrink (deoxyhemoglobin to oxyhemoglobin)

5th coordination site

occupied by an imidazole ring of a histidine called the proximal histidine.

The structural features are similar in myoglobin and hemoglobin for different animals because

of the amino acid sequence (amino acids are conserved between species

______________ is a allosteric stimulator

oxygen

There is a direct correllation between BPG and

p50

Gamma chain does not have as many __________

positive charges

The heme group consists of a organic group, ________________, and a _________________ .

protoporphyrin, central iron ion in the ferrous (Fe2+) form

At normal pH of 7.4

salt bridges do not form between His and Asp.

If the interacting sites bind different ligands

Heterotropic effect

Low P50 signifies

High affinity for oxygen

Allosteric activators binding to a site separate from the functional site leads to

Active (R state)

Describe adult hemoglobin (Hb A)

Adult chain is mainly beta chains, this attracts negatively charged 2,3-BPG.

The fraction of the myoglobin sites bound to the oxygen depends on the ________________ .

Concentration of the free oxygen

Subunits are either all T state or all R state

Concerted model

Once iron is bound to oxgen, what occurs

Conformational change in hemoglobin (cavity shrinks, becomes narrower). This dictates between deoxyhemoglobin and oxyhemoglobin

Describe fetus hemoglobin (Hb F)

Has gamma chain (α2ϒ2), it supports the R state, it has a serine group(LOSING POSITIVE CHARGES) instead of a histidine group, it has low affinity for 2,3-BPG. Oxygen binds more tightly to fetal Hb

If the interacting sites bind ALL the same ligand

Homotropic effect

Allosteric inhibitors binding to a site separate from the functional site leads to

Inactive (T state)

Name some of the functions of myoglobin (3)

Increase O2 solubility in tissues (muscle), Facilitates O2 diffusion, stores O2 in tissues

Look at slide 25 in Lecture 8 to understand variants for sickle cell

Look at slide 25 in Lecture 8 to understand variants for sickle cell

Sickling occurs when

there is a high concentration of deoxy Hb

Oxyhemoglobin is

(R state)

Deoxyhemoglobin is

(T state)

Purified Hb or stripped Hb doesn't have

2,3-BPG

pO2 in the tissue is ______________

20 torr

Iron lies in the middle and can form __________________, and two additional bonds called __________________

4 bonds with nitrogen 5th and 6th coordination sites

Iron in Heme is bound to six sites, what are they?

4 nitrogens, a nitrogen from a proximal histidine side chain on one of the main acids in the protein, and the last coordination site (6th) is available to bind to a O2 molecule.

____________________ is the binding of one ligand to a protein influences the affinities for the ligand of the other binding sites on the protein

Allosteric Effect

Bind to a protein at a site separate from the functional binding site (may be inhibitor or activator)

Allosteric effectors (modulators)

How does a low pH cause more O2 to be released?

At a pH of about 7.2, salt bridges (ionic bonds) form between histidine and aspartic acid. This stabilizes the T state (deoxy) of Hb. Therefore more oxygen can be released.

Allosteric effectors of hemoglobin are: (3)

Biphosphoglycerate, Protons, CO2

Alpha-Thalassemia

Can have 0,1,2,3, or 4 copies of alpha chains Low levels of alpha chains are compensated with gamma or beta tetramers

Stabilizes the T state of Hb (CO2 as an allosteric effector)

Carbamate (salt bridge)

What is an example of an allosteric effect?

Cooperative binding of oxygen in hemoglobin

Distal Histadine, why is it important

Distal histadine is opposite to the proximal histadine. It is responsible for preventing oxidation of Heme iron and reduces CO from binding to heme (Distal histadine is responsible for stabilizing oxygen found in 6th coordination site.

What is pO2?

Fraction of gas phase that is O2 (pressure)

Describe the structure of hemoglobin

Heterotetramer: 2 alpha subunits and 2 beta subunits (M.W.= 64 KDa). Alpha and beta subunits are homologous (similar) to each other and to myoglobin. Myoglobin binds 4 oxygen molecules

β chains have His at central cavity BUT γ chain has serine residues So what does that mean for binding affinity for BPG?

Hb F has a lower binding affinity for 2,3-BPG, therefore, it can bind more tightly to oxygen as oxygen is delivered from the maternal to the fetus

The addition of iron to a protoporphyrin IX ring turns causes the ring to know be known as

Heme (Iron has to be in Fe2+ state)

You want primary oxygen carrier to be _______________. What type of curve will this have?

Hemoglobin Sigmoidal

T form is stabilized by (4 things)

Increase in CO2 Decrease in pH Oxygen being released from heme group Binding of 2,3-BPG

Describe the structure of myoglobin

Monomeric protein (single polypeptide chain), globular protein, intracellular protein (mainly in muscle cells) Myoglobin only binds one molecule of oxygen. Has two components: oxymyoglobin and deoxymyoglobin (16KDa), 78% alpha-helical structure

Higher amounts of CO2 cause what?

More oxygen to be released into the tissues (ex. if two examples have the same pH, but one has a higher pressure of CO2, the one with the high pressure of CO2 will release more O2)

2,3-BPG is __________ and binds to ____________ amino acids between ____________

Negatively charged, positively charged, β subunits

Conformational changes of hemoglobin chain are induced by ___________.

Oxygenation

Partial pressure of O2 required to give 50% saturation.

P50

Sickle cell anemia can lead to ______________________ (can lead to diabetes, heart failure, liver disease)

Secondary hemochromatosis

Binding of S converts only that subunit from T to R

Sequential model

2,3 BPG and CO2 both stabilize ______________

T state

2,3-BPG binds only to ______________

T states

Misfunctioning of hemoglobin genes

Thalassemias (One or more genes coding for hemoglobin have been deleted, one or more genes may be shortened)

Name a function of hemoglobin

Transports O2 from lungs to peripheral tissues (erythrocytes)

Allosteric enzymes have a rapid transition between the ____________________ and the ____________________ conformations

active (R) inactive (T)

Mutation in sickle cell anemia is found on the ____________

beta chain

6th coordination site

binds to oxygen

Whenever _____________ contain one or more oxy subunits, the T----> R transition occurs

both αβ dimers

Structure dictates __________ .

function

Beta chain ________________ after the baby is born

greatly increase

Only ________________ can be in both R and T conformations

hemoglobin

2,3-BPG increases at ____________________

higher altitudes

Decrease in pH (increase in H+ concentration) promotes an _________________

increase in oxygen release

Fe3+ acts as an __________________ to oxygen binding

inhibitor

Activities of allosteric enzymes are changed by ______________ and _________________

inhibitors activators

What structural changes occur when oxygen binds in Hemoglobin?

iron ion moves into the plane, and the proximal histidine, which is part of a alpha helix, moves with the iron.

As 2,3 BPG increases, _____________________

more oxygen goes into the tissues

The binding of oxygen to hemoglobin follows a _____________ curve

sigmoidal

The resulting structural change(from T to R state) is communicated to the other subunits so that:

the two αβ dimers rotate with respect to one another, resulting in the formation of the R state.