Lecture 6 Flashcards
What are the three classes of proteins that allow metal ions into the cell or the blood
Channels (facilitated diffusion of metals into the cell, don’t ever need NRG, passive)
Exchangers (taking na out and letting ca in)
Transporters (exclusively require energy, active transport )
What is iron required for in humans
The biosynthesis of:
Heme containing proteins
Iron sulfur cluster proteins
Iron in enzymes (ex. Ribonucleotide reductase)
What is myoglobin
An oxygen carrier in muscle tissues
What is a heme
It’s a prosthetic group (or cofactor) that carries O2
It’s an iron porphyrin (has iron in centre of some rings)
What is the oxidation state of fe in the heme
2+, if it bind to oxygen is becomes 3+ (because hard ligand)
Why does the heme sit so deep in the myoglobin?
Because it was put there post translationally
What happens if the heme fe binds to carbon monoxide instead of oxygen
C=O is toxic so when it bind in place of oxygen it poisons the heme and oxygen can’t bind anymore
You suffocate
What is hemoglobin
Oxygens carrier in the blood
Has four subunits (tetramer) so it binds four heme groups
What type of binding does hemoglobin show in contrast to myoglobin
What does the inflection point mean
What order reaction is myoglobin
Coorperative ( the affinity of oxygen changes if one heme group is bound to oxygen) shows sigmoidal kinetics
Because one inflection point, this means two site get preferentially occupied then the other two
Myoglobins is a 1st order reaction, has only one subunit so it doesn’t show cooperativity
Know how to draw the heme
Slide four
How is the heme/protoporphyrin made?
There are two steps, one in the cytosol and the other in the mitochondria
Starts with succinyl coa from TCA and glycine
The final step is the insertion of Fe2+ to form the final heme
What does electron transfer protein or redox proteins use for their function
Heme groups or iron sulfur clusters
What is the shape of the heme group and why
It’s very tightly packed and fe is very tightly bound
The heme group is flat and planar because of the tightness
What is cytochrome c and mitochondrial cytochrome oxidase
Mitochondrial Cytochrome oxidase is a heme copper oxidase which reduces O2 to H2O
Cytochrome c with a heme binds to the oxidase to deliver 4 electrons and hydrogen through the pump and allow this redox to happen
Copper is involved
When cytochrome c comes in, the oxygen in its heme gets replaced by copper
What are three different iron sulfur cluster proteins
Ferrodoxin and rubredoxin , aconitase
What always need to happen to iron
It always need to be very tightly bound , cannot be free in the blood
What are the irons surrounded by in iron sulfur cluster
By four Sulfurs which come from cys side chains or elemental sulfur
Ferredoxin has how many clusters
Aconitase
Diff form of ferrodoxin
Rubredoxin
4 fe (cube shape)
3 (broken cube)
2 (flat square)
1
If the heme sulfur clusters are not formed what happens
Many diseases since iron is now free in blood
How are clusters formed
By desulfuration of cys to make elemental sulfur
Then the cluster is made and sent to heme sulfur cluster proteins (HSC)
Then atp dependent insertion of those clusters into recipient proteins
What is ribonucleotide reductase
Converts rna to dna
Is an example of a diiron (3+) cluster
ribonucleotide reductase structure
Has fe surrounded by oxygen, bidentate binding so fe3+
What is special about iron
Essential element for growth/survival of all living organisms
One of the most abundant elements in earths crust
Can be very toxic since it can make oxygen radicles through Fenton chemistry ( which is why only specific amounts of iron can be given to people and why fe is bound so tight)
If high oxygen conditions, iron is found in fe3+ form
In anaerobic conditions or low ph fe2+ (ferrous) is dominant
Fe2+ highly soluble (bound with low affinity 10^-14M, fe3+ is not (10^-18)
What form is fe in in food then when it’s in our bodies
In food it’s fe3+ which then turns to fe2+ in our bodies since oxygen rich
What happens to fe once it’s in our body
Then it’s secreted into the blood where is bound to transferrin as fe3+
This whole transferrin fe3+ complex can be taken up through transferrin receptors
Where is the largest pool of iron found in the body
Why
In the hemoglobin proteins in red blood cells.
This is because iron need to always be in the bone marrow where red blood cells are being made
What recycles red blood cells
Macrohpages. The iron is realeased back and cycle of iron transferrin starts again
What recycles red blood cells
Macrohpages, the. The iron is realeased back and cycle of iron transferrin starts again
Where is iron stored as in the cell, what about in liver
In cell it’s present as 2+
In liver it’s in the ferritin storage protein as fe3+
What is a machine that can measure the exact amount of iron in the tissues
ICP-MS
What are hepatocytes
Liver cells
How many grams of iron in the blood
In hepatocytes
In transferrin iron complex
In gut
What happens to the amount as it goes to different part in the body
2.5g
1g
3mg
1-2mg
Amount gets smaller (more divided up)
What is a gut cell called
Red blood cell
Liver cell
Enterocyte
Erythrocytes
Hepatocyte
How is iron taken up by enterocytes (gut cells)
Fe3+ its first converted to fe2+ then it goes through the DMT (divalent metal ion Transporter) in the cell
It either forms ferritin complex or
Fe2+ is taken out of the cell via jak2, ferroportin and hephastin convert it to 3+
When out of the cell it’s back into fe3+ where it’s bound to transferrin
What is the TfR1 in the hepatocytes
It’s a transferrin receptor
Converts the fe3+ to 2+ for it to go inside the cell
By Reducing
How is iron taken up by macrophage (white blood cell)
Macrophage targets cancer cells by shooting iron at them, which causes oxidative damage through Fenton chemistry
So it’s taken in to the macrophage by rbc transferring it, goes from fe3+ to 2+ inside the macrophage
Can either from the insoluble ferritin storage thing
Or leave the macrophage via ceruloplasmin copper protein turning it into fe3+ to bind to transferrin
How is iron taken up by hepatocytes
It’s already in the tresferrin fe complex
Goes into the cell via tfr1 binding to transferrin and converting its 3+ to Fe2+
Then it can either form ferritin storage or export the iron back out via ceruloplasmin and deliver it to other tissues
What is ferritin
Insoluble iron 3+ clusters mostly found in helatocytes (in liver)
Made up of 24 identical subunits, has a tetrahedral arrangement
The iron sulfur clusters is placed in the middle
Can open up and close so that iron leaches out through the middle
What is transferrin
It transports iron through the serum to the bone marrow where red blood cells are made
Also transports iron from the gut to the liver for storage
How long do red blood cells circulate t
What does this mean
120 day (meaning they’re very stable proteins when bound to iron)
Then they are chewed up by macrophages which store the iron for recycling in our bodies
What is holotransferrin
Apo transferrin
Iron is bound
Ligands not bound
How is iron taken up by cells via the tf cycle
First the apotransferrin (no iron bound) is present.
Once fe3+ bind to give holotransferrin, TFR1 recognizes and binds it.
This TFR1 and holotransferrin are taken into the cell Clathrin coated pits forming an Endosome (still bound in the endosome so still fe3+)
A proton pump on the endosome lowers the pH, this makes the transferrin release iron (now unbound) turning fe3+ to 2+ still
DMT on the endosome transports the fe 2+ iron back out of the endosome
The fe2+ free in the cell cytosol turns into fe-s clusters in the mitochondria OR
Can go into ferritin as fe3+ as storage
How does co2 change HCO3 concentration
If carbonate binds to holotransferrin what happens
Increased co2, lower HCO3
Lower co2, higher HCO3
The solution would turn to a lower pH
What is ferritin
How can we detect liver damage base on ferritin
Can look at how much iron in the blood
Blood turns dark.
What is hepicidin structure
A sulfur rich protein (cysteine rich)
Made of two beta sheets
What is hepicidin structure
A sulfur rich protein (cysteine rich)
Made of two beta sheets
What is hepicidin used for
It’s an iron regulator
So it’s made in the liver in response to high iron, released in the bloodstream, then shuts down iron coming in from the gut and macrophages
Shuts it down by binding to ferroportin
What diseases are caused by too much hepicidin (low iron)
What diseases are caused by too low hepicidin (high iron)
Anemia
Hereditary hemochromatosis
What is the mechanism of hepicidin inhibition intake of iron from enterocytes and macrophages
After hepicidin binds to ferroportin, ferroportin becomes phosphorylated by JAK2 (kinase)
The phosphorylated ferroportin is internalized by the cell and degraded
This stops the efflux of iron into the blood from cells (like macrophage, hepatocytes and enerrocytes)
In the presence of hepicidin jak2 acts as a
Negative regulator
How is hepicidin made to help against bacteria
It’s made in the liver During inflammation in the host
This inflammation making the hepicidin decreases level of iron in the blood which invading pathogenic bacteria use
What is lactoferrin when there is inflammation
It’s secreted by neutrophils and targets the inflammation
Looks like transferrin but binds iron even stronger (so take more iron out of blood during inflammation), which is why it again makes iron less available for bacteria
