description about RBC membrane and its structural peculiarities,how it differs from other cells of our body. How this specialized cell manage homeostasis and function in a well defined manner. This presentation will also help in understanding various RBC storage lesions ,an important aspect of blood banking.

1. D R A K S H A Y A T O M A R
D E P A R T M E N T O F I M M U N O H E M A T O L O G Y A N D
B L O O D T R A N S F U S I O N
A F M C , P U N E
RBC STRUCTURE AND
METABOLISM

2. INTRODUCTION
 RBCs are complex ,metabolically active cells using
glucose to make ATP and reducing equivalents to ensure
flexibility and O2 delivery
 Life span – 120 days
 Neither use O2 for extraction of energy nor synthesizes
protein
 Proteomics has identified 2200 separate proteins in RBC
that are the product of 5% of all human genes

3. RBC MEMBRANE
Erythrocyte membrane that is normal in structure and
function is essential for survival of red cell
 Accounts for the cell's antigenic characteristics
 Maintains stability and normal discoid shape of cell
 Preserve cell deformability
 Retain selective permeability

4. RBC MEMBRANE
 Semipermeable lipid bilayer supported by a meshlike
protein cytoskeleton
 Proteins and phospholipids are organized
asymmeterically.
 Biochemical composition includes 52% proteins,40%
lipids and 8% carbohydrate.

5. MEMBRANE LIPIDS
 Choline containing, uncharged phospholipids, outer
layer:
–Phosphatidylcholine(PC) (30%)
–Sphingomyelin(SM) (25%)
 Charged phospholipids, inner layer:
–Phosphatidylethanolamine (PE) (28%)
–Phosphatidylserine (PS) (14%)- Apoptotic marker of
RBC

7.  Asymmetric phospholipids distribution is maintained by:
–Differential rate of diffusion through membrane bilayer
of choline containing phospholipids (PC and SM diffuse
slowly)
–Charged phospholipids interaction with membrane
skeletal protein.
–Active transport of amino phospholipids (PC and PE)
from outer to inner layer.

8.  This asymmetric phospholipid distribution among
the bilayer is the result of the function of several
energy-dependent and energy-
independent phospholipid transport proteins.

9. MAINTAINENCE OF ASSYMETRY

10. MEMBRANE PROTEINS
 Integral proteins
–Embedded in membrane via hydrophobic
interactions with lipids.
 Peripheral proteins
–Located on cytoplasmic surface of lipid bilayer,
constitute membrane skeleton.
–Anchored via integral proteins
–Responsible for membrane elasticity and stability.

11. INTEGRAL PROTEINS
 Band 3
 Glycophorin
 Aquaporin

12. BAND 3
•Functions:
–Anion transport
 Exchanges bicarbonate for chloride
–Structural:
 Linkage of lipid bilayer to underlying membrane
skeleton.
–Interaction with ankyrin and protein 4.2, secondarily
through binding to protein 4.1.
 Important for prevention of surface loss.

13. GLYCOPHORINS
 Comprise 2% of RBC membrane proteins.
–Sialic acid rich glycoproteins (A,B,C)
 3 domains:
–Cytoplasmic
–Transmembrane: single spanning alpha helix
–Extracellular: glycosylated

15. GLYCOPHORINS
 Human RBCs glycophorins are integral membrane
proteins rich in sialic acids that carry blood group
antigenic determinants and serve as ligands for
viruses and parasites

16. AQUAPORINS
 Aquaporins selectively conduct water molecules in
and out of the cell, while preventing the passage
of ions and other solutes
 Allow RBC to remain in osmotic equilibrium with
extracellular fluid.

17. Sphingomyelin(SM)
Phosphatidylethanolamine (PE)

19. PERIPHERAL MEMBRANE PROTEINS
 Spectrin
 Actin
 Protein 4.1
 Pallidin(band 4.2)
 Ankyrin
 Adducin
 Tropomycin
 Tropomodulin

20. SPECTRIN
Flexible, rod like molecule, 100nm length.
 Responsible for biconcave shape of RBC
 Two subunits:
–Alpha and beta, entwined to form dimers.
–Associate head to head to form tetramers
 End-to-end association of these tetramers with short
actin filaments produces the hexagonal complexes
observed

22. ACTIN
 Short, uniform filaments 35nm in length
 Length modulated by tropomyosin/tropomodulin
 Spectrintail associated with actin filaments
 Approx 6 spectrin ends interface with one actin
filament, stabilized by protein 4.1

23. ANKYRIN
 Interacts with band 3 and spectrin to achieve linkage
between bilayer and skeleton.
 Augmented by protein 4.2.

24. OTHER PERIPHERAL PROTEINS
 Protein 4.1
–Stabilizes actin-spectrin interactions
 Adducin
–Also stabilizes interaction of spectrin with actin.
–Influenced by calmodulin
(thus can promote spectrin-actin interactions as
regulated by intracellular Ca concentration)

25. CHARACTERISTICS OF RBCs
DEFORMABILITY :
 It is controlled by ATP driven membrane
cytoskeleton.
 Loss of ATP leads to decrease in phosphorylation of
spectrin.
 Increase in deposition of membrane calcium.
 Rigid cells are removed from the circulation.

27. PERMEABILITY :
 Permeability properties of the RBC membrane and
the active RBC cation transport prevent colloid
hemolysis and control the volume of RBC.
 Freely permeable to water and anions; relatively
impermeable to cations.
 When RBC are ATP depleted Ca and Na are allowed
to accumulate intracellularly and K and water are
lost.

28. METABOLIC PATHWAYS
 Mainly anaerobic, RBC have to deliver not consume
O2.
 No nucleus/No mitochondria.
 RBC metabolism may be divided into anaerobic
glycolysis and 3 ancillary pathways

29.  RBCs contain no mitochondria, so there is no
respiratory chain, no citric acid cycle, and no oxidation
of fatty acids or ketone bodies.
 The RBC is highly dependent upon glucose as its
energy source.
 Energy in the form of ATP is obtained ONLY from the
glycolytic breakdown of glucose with the production of
lactate (anaerobic glycolysis).


30. RBC METABOLISM
 Glucose transport through RBC membrane:
Glucose is transported through RBC membrane
by facilitated diffusion through glucose transporters
(GLUT-1).

31. GLYCOLYSIS
Importance of glycolysis in red cells:
 Energy production: It is the only
pathway that supplies the red cells
with ATP.
 Reduction of methemoglobin:
Glycolysis provides NADH for
reduction of metHb by NADH-
cytob5 reductase
 In red cells 2,3
bisphosphoglycerate binds to Hb,
decreasing its affinity for O2, and
helps its availability to tissues.

32. UTILIZATION OF ATP
 Phosphorylation of sugars and proteins
 ATPase driven ion pumps
 Maintenance of membrane asymmetry
 Maintenance of red cell shape and deformability
using ATP dependent cytoskeleton

33. METH Hb REDUCTASE PATHWAY
 Maintains Iron in reduced state for effective
transport of O2
 Protect SH group of Hb and membrane proteins
from oxidation

34. LEUBERING RAPOPORT SHUNT
 The hydrogen ion concentration is the most
important physiological modulator

35. LEUBERING RAPOPORT SHUNT
 Binding of 2,3 DPG to DeoxyHb stabilise the tense
state of Hb and favours release of O2

36. LEUBERING RAPOPORT SHUNT
 Free 2,3 DPG also binds with Band 3 and causes
partial detachment of membrane from cytoskeleton
allowing lateral movement of membrane structure.

37. PENTOSE PHOSPHATE PATHWAY
 Production of NADPH – ‘reducing power’
Glutathione is needed in reduced form for:
 Elimination of peroxide
 Protection of proteins SH groups
This shunt also provide ribose 5 phosphate needed for
PRPP ( substrate for adenine nucleotides reqd for
continuing ATP synthesis)

38. PENTOSE PHOSPHATE PATHWAY

39. PATHWAYS

40. HEMOGLOBIN OXYGEN DISSOCIATION
 Dissociation and binding of oxygen by hemoglobin
are not directly proportional to pO2.
Sigmoid-curve.
 It permits a considerable amount of O2 to be
delivered to the tissues with a small drop in O2
tension.

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