NUTR 3210 Study Guide - Final Guide: Heme Oxygenase, Porphyrin, Membrane Transport Protein
28 Apr 2018
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Micronutrients 4
• What’s Iron?
- Found in lots of food at low levels
rich in liver, meats, plant sources
- In food, iron can be found in 2 forms:
heme (within porphyrin ring of hemoglobin + myoglobin)
non-heme – plants
- Only 2 states of iron are stable in the aqueous environment of the body and in
food: Fe3+ (ferric) and Fe2+ (ferrous)
- RDA higher for women due to menses
- UL: 45mg/d leads to hemosiderosis
• What are the functions of iron in the body?
- O2 transport (important for hemoglobin + myoglobin)
- Redox reactions – is an active component of ETC (iron sulfur centers +
cytochrome heme proteins)
- Iron metalloenzymes
• How do the different forms of iron get absorbed?
- Between 10-18% of iron ingested us absorbed; amount absorbed depends on
person’s iron status
1) Non-heme iron:
Reduced before absorbed; we can only absorb Fe2+
HCl & proteases cleave non-heme iron from food components in stomach
releasing mostly ferric (Fe3+) iron
Stomach acid converts most Fe3+ into ferrous Fe2+
Any remaining Fe3+ is reduced by a reductase in the small.I into Fe2+
Fe2+ is transported by divalent metal transporter 1 (DMT1, in small.I)
2) Heme iron:
Released from hemoglobin/myoglobin by proteases in the stomach + small.I
Heme (porphyrin ring) is taken up in the small.I by carrier protein 1 (HCP1)
Inside small intestinal cells, the heme porphyrin ring is briken down by heme
oxygenase into Fe2+ and protoporphyrin
Heme taken as a whole in small.I and proteases break it down to Fe2+
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• What are the factors influencing iron absorption?
- Chelators are small organic compounds that form a complex with a metal ion
Can affect absorption
if iron-chelate is soluble = then absorption is enhanced
if iron-chelate is insoluble = then absorption is inhibited
- Enhancers: vit.C donates e- acting like a reducing agent for ferric iron
- Inhibitors: polyphenols (coffee +tea), oxalic acid (spinach), insoluble fibers
Coffee just after a meal reduces iron absorption by ~50%
Oxalic acid binds with iron (+ other metals), prevents absorption
•
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• What’s the iron distribution and metabolism?
- Iron is transported in blood in Fe3+ form bound to transferrin (carrier protein)
- Why is it important that iron is bound by a carrier?
Prevention of free Fe2+ from accumulation in bloob; unbound Fe2+ iron has
high redox activity = can readily lose an e- = free radicals (interacts with H2O2)
-When iron is high
= from liver
- Prevent iron
from going in
blood, stays in
intestinal cells;
lost when cells die
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Document Summary
Found in lots of food at low levels. In food, iron can be found in 2 forms: Heme (within porphyrin ring of hemoglobin + myoglobin) Only 2 states of iron are stable in the aqueous environment of the body and in food: fe3+ (ferric) and fe2+ (ferrous) Rda higher for women due to menses. O2 transport (important for hemoglobin + myoglobin) Redox reactions is an active component of etc (iron sulfur centers + cytochrome heme proteins) Between 10-18% of iron ingested us absorbed; amount absorbed depends on person"s iron status: non-heme iron: Reduced before absorbed; we can only absorb fe2+ Hcl & proteases cleave non-heme iron from food components in stomach releasing mostly ferric (fe3+) iron. Stomach acid converts most fe3+ into ferrous fe2+ Any remaining fe3+ is reduced by a reductase in the small. i into fe2+ Fe2+ is transported by divalent metal transporter 1 (dmt1, in small. i: heme iron: Released from hemoglobin/myoglobin by proteases in the stomach + small. i.
