iron

Question 1

proteins that contain iron - haemoproteins

Answer 1

• haemoglobin - oxygen binding (oxidases, peroxidases, catalases) - oxygen metabolism

a lot of the body’s iron is contained within the haemoglobin in the body.
- It’s continuously circulating in your red blood cells and it is the way in which we carry oxygen around the body.

Question 2

non-heme - iron-containing proteins

Answer 2

• mitochondrial aconitase - energy metabolism
• Fe-S proteins in electron transport chain - energy metabolism
• ribonucleotide reductase - DNA synthase

Question 3

specialised molecules for iron transport

Answer 3

we have specialized molecules - they are efficient at taking the iron, transporting it around the body, storing it
- and it is a highly coordinated process.
- so dependent on the situation of the individual and then the person’s body and a particular time you are ensuring that you are uptaking sufficient iron, you’re storing and you’re transporting to ensure that you’re delivering iron to where it’s needed.
– So we’re able to in a way, balance. Those mechanisms to ensure that iron is where we need it at a particular time.

Question 4

different types of iron in the body - duodenal absorption

Answer 4

In our diet, We have different types of iron
- some are soluble some are insoluble.
- We generally find fe3 + or heme iron in the diet, and we have absorbed that in the duodenum and
- We absorb around 1 to 2 milligrams per day
- So we should have enough in our dietary intake in order to be able to absorb that
when we take it in then we will either store it Or transport it or use it.

Question 5

liver iron

Answer 5

• liver parenchyma
  -1000 mg

Question 6

muscle - iron

Answer 6

muscle myoglobin - 300 mg

Question 7

bone marrow iron

Answer 7

300 mg

Question 8

reticuloendothelial macrophages

Answer 8

600 mg

Question 9

how do we transport iron

Answer 9

transferrin is the way that we transport the iron to those cells that have a transferin receptor
and that will take the iron in to the cell for utilization.

Question 10

where do we store iron that isnt used

Answer 10

• If we don’t need to use it all so if we want to store some we can store it for example in the liver.
• So the main storage protein for iron is feritin.
  ○ If we have too much iron, we can store it in a pathological form, which is called hemosiderin, but feritin is our main storage protein.

Question 11

where do we use iron

Answer 11

-We can find it in myoglobin in muscles For our muscular activity
○ the main place that we find this being utilized is in the bone marrow.
○ So you’ve got to have a constant production of red blood cells, So those are produced from the bone marrow in the hematocrit stem cell producing fully functional red blood cells, and those contain a lot of iron

Question 12

how is iron broken down

Answer 12

• they will then be broken down. So at the end of their 120 days lifespan, they’ll be broken down by macrophages.
  
  • And that iron will then be recycled and reused and will be transported back to either be stored or used.
• So we’ve got a really nice cycle of iron within the body,
  but we do need to ensure that we have an intake that allows us to maintain that cycle

Question 13

iron excretion

Answer 13

• average 1-2 mg per day
• sloughed mucosal cells, skin loss (desquamation), menstruation, other blood loss
• the level of control is absorption rather than loss and that allows us to maintain that balance.

Question 14

iron handling proteins

Answer 14

recent discovery that iron ‘handling proteins are present in the kidney and that they also help us to regulate the amount of iron that we have in the body

Question 15

iron form that we consume

Answer 15

the inorganic iron we consume is Fe3+ and is insoluble
Fe2+ is known to be the form that is transported

Question 16

transferrin bound iron

Answer 16

when we have transferrin bound iron, it has to be 3+

Question 17

How do we get iron into the body

Answer 17

• We’ve got fe3 Plus in our diet and it’s in this form this insoluble form of fe3 Plus.
• There are certain features within the gut help the conversion of fe3 plus to fe2 plus
• the acidic environment of the gut helps that conversion from fe3 to fe2.
  ○ vitamin C in our diet is also a co-factor - that can also help the process of conversion from fe3 to fe2 Plus.

Question 18

DcytB aka Cybrd1

Answer 18

a ferric reductase expressed in the intestinal mucosa
- in mouse, DcytB is a 286 amino acid protein with 45-50% similarity to cytochrome b561 family of plasma membrane reductases, hence the name duodenal cytochrome b.
- promotes reduction of dietary ferric iron to ferrous iron so it can be. transported across the apical enterocyte membrane.
- Ascorbate (vitamin C) acts as a co-factor
- strongly unregulated when dietary ion is restricted, during anaemia, and in response to hypoxia.
- all are drivers for upregulation of iron acquisition

Question 19

how is iron transported across biomembranes

Answer 19

early studies on non transferring bound iron transport
- uptake into vesicles had the characteristics of a carrier mediated process - it involved transport proteins
- the kinetics of the apical and basolateral transporters differed

Question 20

what protein is used to get iron across the membrane once its been converted

Answer 20

divalent metal transporter 1
- important for moving Fe2+ into the enterocte in the duodenum

Question 21

divalent metal transporter 1

Answer 21

• Km for Fe 2+ - 6 micrometres
  -pH dependent
• transports Cd2+ -> Fe2+ -> Co2+, Mn 2+ -> Zn 2+, Ni 2+, VO 2+ and Pb 2+

Divalent metal transport 1 is vital for the transport of iron into the gut.

Question 22

mouse model without DMT1

Answer 22

So we were able to find out the characteristics of this particular transporter by looking at another a mice model that didn’t have DMT 1 so it lacked this intestinal divalent metal transporter,
- when we removed dmt1, it produces a severe iron deficient anemia in the mice
So therefore the iron wasn’t being transported into the enterocyte, so it wasn’t available for transport around the body in order to produce those red blood cells

Question 23

molecular characteristics of divalent metal transporter 1

Answer 23

• 561 amino acid polypeptide - 60 kDa
• predicted to have 12 membrane spanning domains
• glycosylated extracellular loop
• N- and C- termini in cytosol
• A consensus transport motif in fourth intracellular loop
• Iron responsive element - sensitive to iron - helps to increase the divalent metal transporter synthesis when cellular iron is low and allows us to increase the amount of iron that we intake into the body.

Question 24

DMT1 in the kidney

Answer 24

DMT is mainly found in or on the apical membranes of the early distal tubules in the kidney.
- we may see that there’s reabsorption of iron in that area

Question 25

heme iron

Answer 25

absorbed more efficiently than non - heme iron it might contribute up to about 50% of the iron that we absorb in our diet.

Question 26

haem transporter

Answer 26

the haem transporter is not just specific for that particular molecule. - It also transports folic acid. - folic acid is also needed for healthy production of hemoglobin. So this is a combined transporter - so it also allows us to ensure that we can transport folic acid into the body for production of hemoglobin

Question 27

what happens to iron when it enters the cell

Answer 27

So how does it get from the enterocyte Over the other side across the basolateral side into the circulation. - the fe2 plus binds to something called poly(RC) binding protein and it's basically a Metallo chaperone - So it binds to it and it appears that it mediates the transfer of the free Iron to ferritin. For it to be stored. - But not all of our iron needs to be stored as ferritin, We do need to transport some of it across and we need to be able to take it across this basolateral membrane here into the circulatory system for transport to wherever it is required.

Question 28

basolateral membrane iron transporter - ferroportin/IREG1/ MTP1

Answer 28

only known iron exporter from the basolateral side of the enterocyte - 570 amino acids - ten predicted transmembrane domains -predicted to be a 62 kDa protein

Question 29

functional properties of ferroportin

Answer 29

- mediates saturable and temperature dependent Fe efflux - maximal activity extracellular pH = 7.5 and inactivated at extracellular pH <6.0 - also, mediates efflux of Zn and Co, but not of Cu, Cd, or Mn

Question 30

ferroportin 1a

Answer 30

d ferroportin 1a has a 5 Prime Iron response element.

Question 31

ferrportin 1b

Answer 31

- Ferroportin 1 B lacks that 5 Prime Iron response element and it's not repressed in iron-deficient conditions

Question 32

variants of ferroportin

Answer 32

2 variants of ferroportin - We've got 1 a and 1 B. they allow a balance in Ferroportin and how it moves iron out of the enterocyte having the 2 variants - we find that both of them are expressed in the duodenum And hopefully they will balance. - but they're also found in erythroid tissue which is really important for the production of your red blood cells and the healthy red blood cells - So those are also regulated by the iron content in your diet and the export of iron from the enterocyte into the circulatory system.

Question 33

where is ferroportin localised

Answer 33

localised in the basolateral membrane it is also localized to the basolateral renal proximal tubular membrane. this is evidence again that the kidney is involved in some way in Iron homeostasis

Question 34

hephaestin

Answer 34

A molecule that allows us to transport iron by transferrin - a multicopper oxidase with ferroxidase activity which promotes egress of iron from intestinal enterocytes into circulation by facilitating binding to transferrin heph is a relatively large protein consisting of 1166 amino acids. it is predicted to have one membrane spanning domain

Question 35

function of hephaestin

Answer 35

highest expression is in the small intestine - limited to enterocytes of the villi - almost absent in crypt cells - converts iron (II) state, Fe 2+, to iron (III) state, Fe 3+, and mediates iron efflux most likely in cooperation with basolateral iron transporter, ferroportin 1 - has been detected in colon, spleen, kidney, breast, placenta and bone trabecular cells

Question 36

cellular delivery of iron

Answer 36

pretty much almost all of the cells in your body and tissues in your body will have receptors that will accept iron when we transport it to where it's needed.

Question 37

transferrin

Answer 37

transferrin functions to transport iron between sites of absorption, storage and use transferrin consists of 2 homologous domains each contains one high affinity pH dependent Fe (III) - binding site so we transport iron in the fe3 format.

Question 38

apotransferrin

Answer 38

when we do not have iron bound to transferrin

Question 39

monoferric

Answer 39

fully saturated transferrin

Question 40

transferrin receptor

Answer 40

recognised as the gate-keepers responsible for physiological iron acquisition by most cell types receptor is a disulphie linked transmembrane glycoprotein homodimer. each subunit is 90KDa - And that will accept the transferrin and allow it to be taken into the cell that requires the iron at that particular time.

Question 41

how do transferrin and the transferrin receptor interact with each other

Answer 41

- receptor mediated endocytosis. - we have our fe3 binding to transferrin and the receptor on the cell surface. - there is inwards invagination of the plasma membrane and it forms a vesicle then when it takes in the absorbed substances and it forms an endosome. - Takes in the receptor and the transferrin - This is obviously in our fe3 form. - in order for us to be able to get it out to the other side of the endosome. It will then be transported by a divalent metal Transporter one - But it has to be converted back to fe2 Plus.

Question 42

what converts the iron back to Fe 2+ after the receptor-mediated endocytosis

Answer 42

that is done by STEAP 1 - and it allows it then to be transported across at the dmt1 and it becomes this labile pool. - So it's like a Transit pool. It's neither being transported nor stored, but it's thought to be that it's kind of at a Crossroads of iron metabolism.

Question 43

what happens to Fe 2+ once its in the labile intracellular pool

Answer 43

- it can go a number of different ways. - it can form free radicals so it can be quite dangerous To the body so that labile pool has to be controlled in terms of the levels

Question 44

ferritin

Answer 44

- sequester and store iron. iron is stored as a solid phase mineral - it's a large protein and it's made up of 24 symmetrically related subunits of 2 types - a heavy and a light subunit - inside that ferritin, iron is stored in the ferric state so ferric oxyhydroxide and it's a massive storage protein. - So 1 ferritin molecule can store up to 4 and a half thousand atoms of iron. - ferritin synthesis is inducibe by iron

Question 45

cellular iron balance

Answer 45

- this balance between ferirtin on one side (how much we store) and then the transferrin receptor (how much we are transporting around the body at any one time) so transport versus storage. It can depend obviously on your body requirements and Your body situation So there's quite a lot of things that do actually influence the cellular iron balance.

Question 46

iron balance - when intracellular iron pool is increased

Answer 46

when the intracellular pool is increased. We will want to transport as much iron as we can. We want to be able to transport that out.

Question 47

iron responsive elements

Answer 47

iron-responsive proteins, helps us to control These 2 levels the transferrin receptor and your ferritin.

Question 48

IREs - low iron

Answer 48

- if there are low iron levels that results in increased Iron response proteins which interact with your iron-responsive elements and that inhibit ferritin translation. - So when you have low iron in your body, your body does not want to store iron, We want to transport it. - So this basically blocks any translation here in terms of feritin However, you do want to be able to transport the iron that you have So therefore this is where transferrin receptor production is increased.

Question 49

IREs - high iron

Answer 49

- We will be storing more - therefore high iron- it binds to the iron response protein and that basically stops the translation of our transferrin receptor, but it starts the ferritin production. - the active translation is happening here. - That allows us a place within the body to store that high iron.

Question 50

Hepcidin

Answer 50

it is thought to be the key regulator of our metabolism in the body. - the 25 amino acid protein Hepcidin was first purified from human blood and urine as an antimicrobial peptide and was found to be predominantly expressed in the liver - hepcidin is a repressor of iron absorption - it interacts with ferroportin so that it kind of prevents the iron being able to be transported across that side of the enterocyte into your circulation. - expression of hepcidin is decreased when body iron demands are high

Question 51

orchestration of iron homeostasis

Answer 51

-overexpression of hepcidin leads to iron-adequate anaemia, whereas knockout leads to iron overload - hypothesis is that the liver may be able to control duodenal iron uptake by modulating the amount of circulating hepcidin - increase dietary iron is associated with increased hepcidin. hepcidin then downregulates duodenal iron transport increased hepcidin -> decreased iron absorption

Question 52

regulation by hepcidin

Answer 52

hepcidin can be increased by inflammation, infection. - They can all increase or trigger the increase of hepcidin production and essentially It will decrease the absorption of iron. What's important for us is what the impact might be then in the body - So if you're going to block the absorption, you're essentially can pretty much block all of this happening here so the transport of iron, the storage of iron, the function it can maintain the levels of iron in the body quite nicely for us.

Question 53

hypochromic microcytic anaemia

Answer 53

- hypochromic means They're pale - it lacks colour ○ so you've got a very pale Center here and you've got a very thin rim of nicely stained sort of hemoglobin. - Microcytic - smaller cell in comparison to your normal red blood cell - mean cell volume below 80 centiliters - most common anaemia

Question 54

hypochromic macrocytic anaemia

Answer 54

- Cells larger than normal They will not be fully functional there may be issues with their hemoglobin concentration

Question 55

response to low iron - hypoxia inducible factor

Answer 55

if you have low iron, you will have low oxygen delivery -your hemoglobin concentration and the iron contained within defines the amount of oxygen you can carry around the body. - So if you have a low haemoglobin you have low iron you are essentially at risk of hypoxia. - So this particular hypoxic inducible factors were found and it responds to the low oxygen and the low iron s -the iron response elements, will respond to that low iron also and in combination with the low oxygen, this will essentially trigger the transcription of genes That are involved in a number of processes, but the process were interested in is erythropoiesis - so it will trigger the production of epo within the kidney.

Question 56

the response of the hypoxic inducible factor 2 Alpha, in conjunction with the hypoxia response

Answer 56

the response of the hypoxic inducible factor 2 Alpha, in conjunction with the hypoxia response element Alongside the little iron affecting the iron response protein and iron response Element - These will then trigger the synthesis of epo which will then feed forward into the eryhtropoetic process taking place in the bone marrow. - Hopefully increase the production of erythrocytes

Question 57

low iron - production of ErfE

Answer 57

- because we have this low iron being detected we want to increase the absorption and to ensure that hepcidin is not influencing the absorption of iron in the gut. - so we have the production of something called ErfE which can act on hepcidin ○ that comes from the bone marrow and that blocks the translation or synthesis of hepcidin, which then allows us in the duodenum to be able to take up The iron and be able to transport it by ferroportin Across the basolateral membrane.

Question 58

epithelial response to low iron

Answer 58

at the epithelia the net result of increased HIF alpha is to increase the expression of DcytB, DMT1 and FPN1 in the duodenum and inhibit hepcidin production. more Duodenal cytochrome B, which allows us to convert more fe3 to fe2 plus ore dmt1 which allows so transport more iron across the membrane then we have increased expression of ferroportin 1 at the basolateral side and that allows us to then obviously transport more iron around the body - And it also inhibits pepsin, which we now know controls the absorption at that basal side through ferroportin

Question 59

effects of high altitude

Answer 59

we've got 21% oxygen available to us in the atmosphere, but it's obviously going to be dependent on the oxygen in the air. - Oxygen in the air decreases the higher the altitude - So your body must adapt to that low oxygen. So your body needs to adapt to that particular level of oxygen in the blood and therefore needs to ensure that you have sufficient red blood cells in order to carry that amount around And that's where again we have this response element within the body.