Chapt. 44

1
Chapt. 44

• Ch. 44 Biochemistry
• of Erythrocytes
• Student Learning Outcomes
• Describe the structure/ function of blood cell
  types
• Erythrocytes, leukocytes, thrombocytes
• Explain the metabolism of the red blood cell
• Explain basics of hematopoiesis from bone marrow
• Describe some errors of hemoglobin function,
  anemias, hemoglobin switching
• Describe the structure/ function of blood group
  antigens (Ch. 30)

2
Blood cells

• Table 1 Blood cells (cells/mm3)
• Erythrocytes 5.2 x 106 men
• carry oxygen 4.6 x 106 women
• Neutrophils 4300
• granules phagocytic, O2 burst kills
• Lymphocytes 2700
• immune response, B- and T-cells, NK
• Monocytes 500
• macrophages for bacteria, damage
• Eosinophils 230
• granules destroy parasites (worms)
• Basophils 40
• granules hypersensitivity, allergic
• histamine, proteases,

3
Hematopoiesis

• Hematopoiesis
• Stem cells in bone marrow (1/105)
• Proliferate, differentiate, mature
• by growth factors, hormones
• signal transduction paths
• Myeloid, lymphoid lines
• Leukemias immature cells
• keep proliferating
• defined by cell type

Fig. 15
4
Anemia

• Anemias hemoglobin concentration is low
• Normal Hb g/dL men 13.5-17.5 women 11.5-15.5
• Anemias classified by red blood cell morphology
• Rbc morphology functional deficit possible cause
• Microcytic, impaired Hb
  thalassemia, lead,
• hypochromic synthesis iron deficiency
• Macrocytic impaired DNA vit B12 or folic
  acid
• normochromic synthesis deficient,
  erythroleukemia
• Normocytic red cell loss acute bleeding,
• normochromic sickle cell defects

5
Erythrocyte metabolism

• Erythrocyte metabolism Only glycolysis
• ATP for Na/K, Ca2
• HMP shunt makes NADPH
• G6PD is 1st enzyme
• Lifetime rbc by G6PD activity
• 2,3-BPG modulates O2 binding
• Need Fe2 Hb bind O2
• If ROS made Fe3, NADH can reduce

Fig. 1
6
Heme synthesis

• Heme synthesis in erythrocyte precursor
• Heme porphryn ring, coordinated to Fe
• Complexed to proteins in hemoglobin, myoglobin
  and cytochromes most common porphryn in body
• 4 pyrrole rings with CH- joining
• Various side chains
• Heme is red color

Fig. 2
7
Heme synthesis

• Heme synthesis
• Glycine, succinyl CoA form
• d-Aminolevulinic acid
• (d-ALA)
• Each heme needs 8 of each
• Final step is Fe2
• Heme regulates
• inhibit 1st enzyme
• repress synthesis
• Porphyria diseases from
• defective enzymes
• intermediates accumulate
• photosensitive, toxic products

Fig. 3
8
Heme synthesis

• Heme synthesis begins with d-ALA
• Decarboxylation by d-ALA synthase
• PLP is pyridoxal phosphate
• Dehydratase joins 2 d-ALA
• 4 pyrroles form porphyrinogen

Fig. 4
9
Sources of iron and heme

• Iron is essential from diet 10-15 mg/day
  recommended
• Iron is not readily absorbed from many sources
• Iron in meats is form of heme, readily absorbed
• Nonheme iron of plants not as easily absorbed
  becauuse other compounds precipitate iron
• Iron absorbed in ferrous state (Fe2), oxidized
  by ferroxidase to Fe3 for transport
• Apotransferrin binds Fe3 Transferrin
• Stored as ferritin in cells
• Heme stimulates synthesis of globin proteins from
  ribosomes

10
Iron metabolism

• Iron metabolism
• Transferrin carries Fe3 to cells stored as
  ferritin
• Transferrin taken up by R-mediated endocytosis
• Hemosiderin stores excess

Fig. 6 RE reticulo-endothelial system
11
Degradation of hemoglobin

• Heme is degraded to bilirubin
• Bilirubin is congugated to glucuronate (more
  soluble),excreted
• Rbc only live 120 days
• Globin is degraded to amino acids

Figs. 7,8
12
Red blood cells

• Erythrocyte cell membrane
• Red disc, pale center
• Biconcave shape
• Maximizes surface area
• 140 um2 vs. 98 um2 sphere
• Deforms to enter tissues
• Spleen destroys damaged
• red blood cells

Fig. 9
13
Cytoskeleton of erythrocyte

• Erythrocyte cytoskeleton
• provides shape, structure, permits stretch
• 2-D lattice of proteins links to membrane
  proteins
• spectrin (a, b)
• actin
• ankyrin
• band 4.1
• membrane proteins
• glycophorin
• band 3 protein
• Mature rbc does not synthesize
• new proteins
• Gets lipids from circulating LDL

Fig. 10 general side view inside cell view up
14
Agents affect oxygen binding of hemoglobin

• Agents affect oxygen binding of hemoglobin
• 2, 3-BPG (glycolysis intermediate) binds between
  4 subunits of Hb, lowers affinity for O2,
  releases O2 to tissues
• Proton (Bohr) effect ?H lowers affinity of Hb
  for O2
• CO2 can bind to Hb (not only bicarbonate)

Fig. 11,12, 14
15
Effect of H on oxygen binding to Hb

• Effect of H on oxygen binding to Hemoglobin
• Tissues CO2 released ? carbonic acid, H
• H bind Hb ? release O2 to tissues
• Lungs reverse O2 binds HHb ? release H
• H2CO3 forms, releases CO2 to exhale

Fig. 13
16
Hematopoiesis

• Hematopoiesis
• Stem cells in bone marrow
• proliferate
• differentiate
• mature
• myeloid vs. lymphoid
• Stromal cells secrete
• growth factors
• Cytokines signal via
• membrane receptors

Fig. 15
17
Bone marrow

• Bone marrow stromal cells secrete growth factors
• Hematopoietc stem cells respond

18
Hematopoiesis involves cytokine signaling

• Growth factors signal through membrane receptors
• Ligand causes receptors to aggregate
• Activates JAK (kinases) by phosphorylation
  (cytoplasmic RTK)
• JAK phophorylates cytokine receptor on Tyr
• Other signaling molecules bind, including STAT
  (signal transducer and activator of
  transcription) ? nucleus transcription
• Also RAS/Raf/MAP kinase activated
• Overactive signal ? cancer
• Transient signal
• SOCS silences

Figs. 16 11.15
19
Erythropoiesis

• Erythropoiesis
• Erythropoietin from kidney increases red blood
  cell proliferation (if low oxygen)
• Reticulocytes still have ribosomes, mRNA to make
  Hb
• Mature in spleen, lose ribosomes
• Make 1012 rbc/day
• Anemia if not
• appropriate diet
• Iron, vitamin B12, folate

Fig. 17
20
Hemoglobin genes

• Hemoglobinopathies, hemoglobin switching
• Order of genes parallels development, controls
• gt700 mutant Hb (often base subsittution)
• HbS sickle cell (Hb b Glu6Val)
• HbC (Hb b Glu6Lys)
• Both ? malaria resistance

Fig. 18
21
Thalassemias

• Thalassemias unequal production of a, b of Hb
• need ab 11
• a has 2 genes each chromosome b only 1
• can have amino acid substitutions, promoter
  mutations, gene deletions, splice
• Improper synthesis cause instability, or
  aggregation
• b has some b b0 makes none
• People offten survive if hereditary persistence
  of fetal hemoglobin HPFH (a2g2 HbF)
• Treatments of b-thalassemia or sickle cell
• increase Hb g transcription

22
VI. Hemoglobin switching

• Hemoglobin switching
• embryo blast synthesis yolk
• fetus liver synthesis
• adult bone marrow
• Multiple genes for Hb
• Order of genes parallels development
• Problems if deletions, other mutations
• Problems if imbalance

Fig. 18
23
Transcription factors control Hb switching

• a-globin locus about 100 kb HS40 control region
• b-globin locus has LCR control region
• Promoter of g gene has many transcription factors
  that bind HPFH mutations often map promoter
• Mutated repressor (CDP) or site
• SSP and SP1 compete for binding near TATA

Fig. 19
24
Blood types reflect erythrocyte glycolipids

• Blood group substances are glycolipids or
  glycoproteins on cell surface of erythrocytes
• Glycosyltransferases add sugars, detemine blood
  type
• Two alleles (three choices) iA, iB, i
• Produced in Golgi, lipid part of membrane of
  vesicle, fuses and carbohydrate extends
  extracellular

Fig. 30.16,17
25
Key concepts

• Key concepts
• Blood contains distinct cell types
• Erythrocytes transport O2 and return CO2 to lung
• Limited metabolism
• Heme synthesis in rbc precursos
• Oxygen binding
• Hematopoiesis from bone marrow
• Leukocytes include monocytes, polymorphonuclear
• Hemoglobin mutant proteins, expression

26
Review question

• Review question
• A compensatory mechanism to allow adequate oxygen
  delivery to tissues at high altitudes, where
  oxygen concentrations are low, is which of the
  following?
• Increase in 2,3-bisphosphoglycerate synthesis by
  rbc
• Decrease in 2,3-bisphosphoglycerate synthesis by
  rbc
• Increase in hemoglobin synthesis by rbc
• Decrease in hemoglobin synthesis by rbc
• Decreasing the blood pH