Biochemistry of Blood Elements 624

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Biochemistry of Blood Elements624

• Vladimíra Kvasnicová
• modified and reduced by Eva Samcová

The figure is found at http//www.biosbcc.net/dooh
an/sample/htm/Blood20cells.htm (March 2007)
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Blood Elements Count

• erythrocytes 4 - 6 x 106 / ?l
• thrombocytes 150 - 400 x 103 / ?l
• leukocytes 4 - 9 x 103 / ?l
• neutrophils 47 - 75
• eosinophils 1 - 4
• basophils 0 - 1
• lymphocytes 23 - 45
• monocytes 2 - 11

hematocrit muži 42-52 ženy 37-47
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2,000,000 erythrocytes / sec into circulation

• The lifetime of erythrocytes (red blood cells -
  RBC) is 120 days New erythrocytes
  reticulocytes - contain more ribosomes and
  components of ER
• The life span of erythrocytes can be dramatically
  reduced in the case of a series of hemolytic
  anemia (in hemolytic anemia occurs increasingly
  hemolysis destruction of red blood cells)
• The production of red blood cells is regulated by
  erythropoietin (EPO) - synthesized in the kidney
  

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What to study

• Erythrocyte structures
• Erythrocyte - metabolism
• Hemoglobin. Structure of hemoglobin
• Saturation curve
• Function of erythrocytes Gas transport

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Red Blood Cells(erythrocytes)

• Structure
• large surface (diffusion of gases)
• cytoskeletal proteins (elasticity)
• membrane as an osmometer (Na/K-ATPase)

The figure is found at http//www.biosbcc.net/dooh
an/sample/htm/Blood20cells.htm (March 2007)
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Red Blood Cells(erythrocytes)
membrane and cytoskeletal proteins
hereditary spherocytosis
The figures are found at http//www.wadsworth.org/
chemheme/heme/microscope/pix/spherocytes_nw.jpg
and http//www.mie.utoronto.ca/labs/lcdlab/biopic/
fig/4.23b.jpg (March 2007)
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Red Blood Cells(erythrocytes)

• membrane transporters
• Na/K-ATPase (active transport)
• GLUT-1 (insulin independent)
• anion exchanger band 3 protein (Cl-/HCO3-)

• membrane antigens
• blood groups

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Membrane antigens example ABO system
The figure is found at http//www.life.umd.edu/cla
ssroom/bsci422/mosser/ABO.gif (March 2007)
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Red Blood Cells(erythrocytes)

• Metabolism
• Erythrocytes lack mitochondria and other
  organelles-reduced metabolism. They degrade
  externally supplied glucose into lactate via
  glycolysis
• Thus glucose is the only energy substrate
• 90 anaerobic glycolysis (2 ATP, lactate Cori
  cycle 2,3-BPG)
• 10 hexose monophosphate pathway (NADPH ?
  antioxidative mechanisms)

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Glucose 6-Phosphate DehydrogenaseGenetic
Deficiency or Presence of Genetic Variants in
Erythrocytes

• Enzyme catalyzes the oxidation of G6P to
  6-phosphogluconate and the reduction of NADP
  in major pathway of NADPH production pentose
  cycle
• NADPH maintains glutathione in its reduced state
• GSH is necessary for the integrity of the
  erythrocyte membrane cells more susceptible to
  oxidative damage by reactive oxygen species - to
  hemolysis.
• One of the most common enzymopathies.100 milion
  people suffer from this deficiency particularly
  in the area Tropical Africa, Mediterranean
  region, some parts of Asia and the Black
  Population in America.
• Result is usually hemolytic anemia. 300 known
  genetic variants of this enzyme wide range of
  symptoms.

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Cori cycle
and muscle
The figure was accepted from Devlin, T. M.
(editor) Textbook of Biochemistry with Clinical
Correlations, 4th ed. Wiley-Liss, Inc., New York,
1997. ISBN 0-471-15451-2
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Red Blood Cells

• Function
• erythrocyte as a bag for hemoglobin
• O2 ? transport, reactive oxygen species (ROS)
• CO2 ? transport, formation of HCO3-
• H ? transport, maintaining pH (35 of blood
  buffering capacity)

• superoxide dismutase
• catalase
• glutathione peroxidase antioxidative
  system
• glutathione reductase
• methemoglobin reductase

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• antioxidative enzymes
• superoxide dismutase (SOD)O2 O2 2 H ?
  H2O2 O2
• catalase (CAT)H2O2 H2O2 ? 2 H2O O2
• glutathione peroxidase (GPx)2 GSH H2O2 ?
  GS-SG 2 H2O2 GSH R-O-OH ? GS-SG H2O
  ROH
• glutathione reductaseGS-SG NADPHH ? 2 GSH
  NADP
• methemoglobin reductase - in erythrocytesHb-Fe3
  e- ? Hb-Fe2 (coenzyme NADH or NADPH)

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glutathione reductase GS-SG NADPHH 2 GSH
NADP
redox buffer
Hexose Monophosphate Pathway
The figure is found at http//www.med.unibs.it/ma
rchesi/ppp.html (March 2007)
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Structure of hemoglobin

• hemoprotein (complex protein globin prosthetic
  group)
• quaternary structure 4 subunits
• prosthetic group of each of the subunit heme
• 4 polypetide chains
• 4 molecules of heme
• 4 ferrous (Fe2) ions

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Mr 64 500
The figure is found at http//dtc.pima.edu/biolog
y/202alpha/lesson1/hemoglobin.jpg (March 2007)
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Pyrrole
hemoglobin
The figures are found at http//www.medical-defini
tions.net/images/hemoglobin.jpgand
http//omlc.bme.ogi.edu/spectra/hemoglobin/hemestr
uct/heme-struct.gif (March 2007)
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Saturation of hemoglobin by oxygen

• quaternary structure of hemoglobin
• allosteric effect
• T-conformation lower affinity to O2 (deoxy Hb)
• R-conformation higher affinity to O2 (oxyHb)
• T ? R
• HHb O2 ? HbO2- H

the saturation curve has sigmoidal shape
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Types of hemoglobin and its subunits

• ?/? thalassemia
• sickle-cell anemia (HbS)
• congenital methemoglobinemia (HbM)

• adult hemoglobin HbA1 ?2?2 HbA2 ?2?2 (? 2
  from total Hb of adults)
• fetal hemoglobin HbF ?2?2 ! higher
  affinity to O2 than HbA !
• binds oxygen more firmly at lower pO2 (placenta!)

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The figure is found at http//www.labcorp.com/data
sets/labcorp/html/img/fethgb.jpg (March 2007)
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Synthesis of hemoglobin

• bone marrow
• in erytroblasts, not in erythrocytes
• 4 individual subunits are connected by
  noncovalent bonds to form tetramer of Hb
• hemoglobin is an intracellular protein within
  ery
• concentration of Hb in blood
• female 120 162 g/l
• male 135 172 g/l

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Synthesis of hemoglobin

• Disorders
• THALASSEMIA group of genetically determined
  disorders absence or reduced synthesis of a
  globin chain (? or ? thalassemia)
• ANEMIA ( decreased oxygen-carrier capacity of
  blood)
• Hemolytic anemia is a condition in which red
  blood cells are destroyed and removed from the
  bloodstream before their normal lifespan is over.
• sideropenic anemia insufficient concentration
  of Fe
• sickle cell anemia point mutationin the
  ?-globin gene forms abnormalHbS (Glu ? Val)

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Transport of blood gases

• Air composition
• 78 N2 21 O2 1 water, inert gases, CO2
  (0,04)
• Air pressure
• 1 atm 101 325 Pa ( 101 kPa) 760 Torr (
  mmHg)
• 1 mmHg 0,1333 kPa
• 1 kPa 7,5 mmHg

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Transport of blood gases

• arterial blood venose blood
• pO2 13,33 kPa 5,33 kPa
• 100 mmHg 40 mmHg
• pCO2 5,33 kPa 6,13 kPa
• 40 mmHg 46 mmHg
• (alveols)

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Transport of blood gases- function of hemoglobin
-

• it transports O2 and part of CO2 (and CO)
• it binds H (reacts as a buffer)
• O2 and CO bound to Fe2 in heme ? 4 O2 / 1 Hb
• oxyhemoglobin HbO2 /carbonylhemoglobin COHb
• CO2 is bound to globin! (-NH2 of side chains of
  amino acids)
• carbaminohemoglobin HbCO2
• H is bound to residues of His
• deoxyhemoglobin HHb

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Transport of blood gases- transport of CO2 -

• largely in a form of HCO3- ( 70)
• CO2 H2O ? H2CO3 ? HCO3- H
• enzyme carbonic anhydrase spontaneous
  dissociation
• (in erytrocytes)
• bound to hemoglobin ( 23)
• freely dissolved ( 7)

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The figure is found at http//fig.cox.miami.edu/c
mallery/150/physiol/sf41x11.jpg (March 2007)
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Transport of blood gases - reactions in
erytrocytes -

• tissues
• CO2 H2O ? H2CO3 ? HCO3- H
• H HbO2- ? HHb O2 ? aerobic metabolism
• (HCO3- formed in the erythrocyte is then
  transported to plasma by an anion exchanger in
  exchange with Cl- this process is called
  Hamburgers effect or chloride shift in the
  lungs HCO3- is transported back into the
  erythrocyte by the same exchange with Cl-)
• lungs
• HHb O2 ? HbO2- H
• H HCO3- ? H2CO3 ? H2O CO2 ? excreted

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O2
O2
The figure is from http//science.kennesaw.edu/jd
irnber/Bio2108/Lecture/LecPhysio/42-29-BloodCO2Tra
nsport-AL.gif (March 07)
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Hemoglobin saturation curve- saturation with
oxygen -
The figure is found at http//employees.csbsju.edu
/hjakubowski/classes/ch331/bind/MbHbbindcurve.gif
(March 2007)
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Right shifted oxygen is more easily released
from Hb but worse bound to it
The figure is found at http//dr-amy.com/rich/oxyg
en/fig1.gif (March 2007)
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Saturation of hemoglobin with oxygen

• Factors affecting the saturation
• alkaline pH and ? pO2 stabilize
  R-conformation(IN LUNGS)
• acidic pH, ? pCO2, ? temperature and 2,3-BPG
  stabilize T-conformation, i.e. deoxyHb(IN
  PERIPHERY)
• shift of the saturation curve toward right

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Bohrs effect the saturation of Hb by O2 lowers
because lowering pH (shift toward right)
The figure is found at http//employees.csbsju.ed
u/hjakubowski/classes/ch331/bind/MbHbbindcurve.gif
(March 2007)
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Patological forms of hemoglobin

• methemoglobin (over 3) metHb
• Fe3 instad of Fe2
• unable to transport oxygen !!!
• glycohemoglobin (over 6) HbA1c
• after long term increased glycemia (Glc bound to
  Hb)
• carbonylhemoglobin (over 2) COHb
• after CO poisoning
• sulfhemoglobin, cyanhemoglobin
• poisoning by H2S, HCN or by cyanides

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Carbon monoxide poisoning

• CO has 200x higher affinity to Hb than O2
• it forms COHb carbonyl hemoglobin(formerly
  called carboxyhemoglobin)
• max. allowed concentration in the air 0.003
• intoxication by CO depends on pCO and a time of
  its exposition (0.04 ? strong headache, 2-3
  hours unconsciousness 1 ? death after a few
  minutes)

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The figure is found at http//dr-amy.com/rich/oxyg
en/fig1.gif (March 2007)
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Carbon monoxide poisoning

• may result due to
• exposure to automobile exhaust
• smoke inhalation
• an improperly ventilated gas heater
• or other appliance
• incomplete burning(incomplete oxidation of
  organic material)

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Saturation of hemoglobin with CO
COHb / total Hb (ratio in )
physiological value ? 2
The figure is found at http//www.uhseast.com/1342
21.cfm (March 2007)
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Carbon monoxide poisoning

• TREATEMENT
• fresh air
• exposure to high concentrations of oxygen (the
  100 oxygen is administered by a face mask)
• it is recommended in patients who have a history
  of loss of consciousness, carbonyl hemoglobin
  saturation greater than 25, metabolic acidosis
  and cerebellar findings on neurologic exam