erythrocyte membrane structure

Eric NiederhofferMedical Biochemistry

What affects the normal functions of an erythrocyte?

A 4-year-old African boy is brought in by his adoptive parents who say that he has pain in his limbs and

does not want to walk

Red Blood Cell: Biochemistry and Sickle Cell Disease

• RBC structuresize, spectrin, channels

• Metabolismglycolysis (2,3-BPG), pentose phosphate pathway (G6PDH, NADPH), glutathione

• Hemoglobingenes, heme, Mb/Hb (normal), HbS (defect), fibers (sickling and inflammation),

thalassemia

An Erythrocyte (RBC)

Reference RangesRBCs, male 4.3-5.9 x 106/µL female 3.5-5.5 x 106/µLHb, male 13.5-17.5 g/dL female 12.0-16.0 g/dLHct, male 41-53% female 36-46%MCV 80-100 fLMCH 25.4-34.6 pgMCHC 31-36 %RDW 11-14.5 %

Practical Values65% of Fe in Hb1 g Hb = 3.46 mg Fe1 mL blood at 15 g/dL Hb = 0.5 mg FeRBC x 3 = HbHb x 3 = HctMicrocytic < 80 fLMacrocytic > 100 fL

Erythrocyte Membrane Composition

http://www.ruf.rice.edu/~bioslabs/studies/sds-page/rbcmembrane.html

RBC Metabolic Pathways

2,3-BPG

BPG mutase

2,3-BPG phosphatase

PPP

NADPH

6PG

3-7 C metabolites(R5P, F6P, G3P)

G6PDHlactonase6PGDH

CO2

NADP+ + H+

GSH

GSSGGR

GP

H2O2 H2O

Glc

Pyr

G6P

1,3-BPG

3PG

HK

PGI

PK

F6P

G3P

PFK

aldolaseF16BP

DHAP

2PG

PEP

PGK

PGM

enolase

G3PDH

Glycolysis

LactateNo O2

LDH

Hemoglobin Genes and Gene Products

http://www.mun.ca/biology/desmid/brian/BIOL3530/DB_Ch09/fig9_24.jpg

Hemoglobin Gene Product Production

Mehta, A. B., and A. V. Hoffbrand. 2000. Haematology at a glance, Blackwell Science, Malden, Mass.

HbF: 2α and 2γHbA1: 2α and 2β

HbA2: 2α and 2δHbE: 2ζ and 2ε

Yolk sac Liver Spleen Bone marrow

Myoglobin and Hemoglobin Structure

deoxyHbdeoxyMb

oxyHb (HbO2)

O2

O2

O2

O2

Glu6→Val6

Glu6→Val6

oxyMb (MbO2)

O2

Hemoglobin Structure Changes

http://www.mfi.ku.dk/PPaulev/chapter8/images/8-3.jpg

Sickle Cell Disease

http://www.emedicine.com/ped/TOPIC2096.HTM

Rare combinations of HbS with HbD Los Angeles, HbO Arab, G-Philadelphia, among others

(>6 major genotypes)at least 1 sickle gene, hemoglobin S (HbS) ≥ 50% Hb present.

homozygotic HbSS (sickle cell anemia) - HbS = 100% Hb present

HbSbeta-0 thalassemia - Severe double heterozygote for HbS and beta-0 thalassemia; almost indistinguishable from sickle cell anemia phenotypically (MCV low)

HbSC disease - Double heterozygote for HbS and HbC, with intermediate clinical severity

HbS/hereditary persistence of fetal hemoglobin (S/HPHP) - Mild form or symptom free

HbS/HbE syndrome - Rare and generally mild clinical course

Hemoglobin Electrophoresis

http://themedicalbiochemistrypage.org/hemoglobin-myoglobin.html

Homozygous HbS

Normal neonate

Normal adult

HbSC

Heterozygous HbS

Relative protein charge

Start (samples applied here)

Anode (+)

Cathode (-)

Molecular Changes of HbS

http://www.sicklecellinfo.net/fiberformation.htm.Daniel J. Harrington, D. J., K. Adachi, and W. E. Royer, Jr. 1997. J. Mol. Biol. 272(3):398-407

Heme

Val

Molecular and Cellular Changes of HbS


Decreased PO2

Permanent damage to RBC

Cell endothelium interactions⟺

Effects of Therapy with Hydroxyurea


Thalassemiasα-thalassemia

β-thalassemia

HbH (β4)

Hb Barts (γ4)

Review Questions

• What proteins compose the membrane of erythrocytes?• What metabolic pathways are used in erythrocytes?• What is hemoglobin; what changes with sickle cell

disease?• What clinical observations would you make concerning

patients with SCD?• What are the thalassemias?

erythrocyte membrane structure

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