Erythrocyte Biochemistry Flashcards
Overall Hb structure
Tetramer with 2 a-chains and 2 b-chains. Contains Fe2+ subunit. Hydrophobic.
HbS and HbF
Research ongoing to induce expression of HbF via hydroxyurea to address inflammation. However, HbF is a toxic chemotherapeutic agent.
Proximal and distal Histidines
Proximal: F8. Bound to heme.
Distal Histidine: E7. O2 binds to the iron between the heme and distal His.
Oxygen dissociation curves
Mb: hyperbolic.
Hb: sigmoidal (due to interactions between globin subunits).
Hb has 2 affinity states. Binding of O2 is reversible.
Positive cooperative binding
Hb binding O2 facilitates binding of another O2. A conformational change allows accommodation for another O2.
The Bohr Effect
Binding affinity of Hb for O2 decreases as pH decreases.
His picks up H+ from tissue causing release of O2.
Modulation by 2,3-BPG
Reduces O2 affinity so Hb gives up more O2 to tissues. Signals to Hb to let O2 go. Shifts ODC right.
ODC in HbF
HbF does not bind 2,3-BPG well, increasing its affinity. Shifts curve to the left. O2 flows from mother to fetus.
Storage Iron
Ferratin: water soluble.
Hemosiderin: water insoluble.
Absorption of Iron
Fe cannot freely diffuse across membrane; involves 5 proteins.
Proteins involved in uptake of Fe (5)
Ferric reductase DMT1 Ferroportin Hephaestin Transferrin
Ferric reductase
Converts Fe3+ (in non-heme iron) to Fe2+.
DMT1 (divalent transporter-1)
Takes up Fe2+
Ferroportin
Forces iron out of cell.
Hephaestin
Converts free iron to Fe3+.
Transferrin
Transports iron in blood.
Fe2+ and Fe3+
Dietary iron is Fe3+, but needs to be Fe2+ to enter the cell. Once Fe2+ leaves the cell, it is converted to Fe3+ so it can be carried to the bone marrow.
Transferrin receptor (TfR) mediated endocytosis
Clathrin coated pits take in iron, and transport to the mito via endosome.. DMT1 transports iron out of endosome.
Hereditary hemochromatosis
Organ dysfunction due to iron overload. Caused by poor regulation of iron uptake and export by enterocyte.
Hepcidin
Regulated uron homeostasis.
Binds ferroportin, causing it to become internalized where it is destroyed.
When iron level is high:
Hepcidin expression is up, ferroportin levels are down, iron absorption is low.
When iron level is low:
Hepcidin expression is down, ferroportin levels up, iron absorption is high.
Regulation of hepcidin expression
If Hfe is mutated, it cannot bind TfR2.
Therefore, it cannot turn on hepcidin expression, so there is no control over ferroportin activity.
RBC production dependent on (2)
Vit B12
Folate
Megaloblastic anemia
Anemia due to Vit B12 and folate deficiency.
Characterized by large RBCs. Have normal Hb content in relation to size.
Structure of folate (3 parts)
- Pteridine: N containing ring.
- PABA
- Glu residue chains.
Pernicious anemia
Type of megaloblastic anemia from vit B12 deficiency due to lack of intrinsic factor.
Occurs in the elderly and may involve an autoimmune disease.
Folate metabolism
Folate —> FH2 —> THF (both via dihydrofolate reductase).
THF can become methylene, methynyl or formyl.
Methylene can become methyl which require B12 to become THF again. Formyl goes to de novo synthesis of pyrimidines.
Vitamin B12 absorption
B12 + R-binder (from gastric mucosa cells) combine.
Proteases cleave to free B12.
Intrinsic factor (from parietal cells) bind B12 and bring to ileum.
Schilling Test part I
Pt given labeled Co and trace unlabeled Co.
Urine collected after 24 hrs.
If there is not radioactive Co, then B12 is not absorbed (continue to part II).
If there is radioactive Co, then there must be a dietary deficiency.
Schilling Test part II
Give radioactive Co and intrinsic factor.
Evaluate urine after 24 hrs.
If Co is absent in urine, it is due to lack of intrinsic factor and pt has pernicious anemia.
Components of embryonic, fetal and adult Hb and production graph.
Embryonic: Gower I, Gower II, Portland. Fetal: a-2, y-2. Adult: a-2, b-2. can have a-2, d-2. Draw graph.
