1. Structure, function, and metabolism of hemoglobin
Vladimíra Kvasnicová

2. 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

3. Mr =
The figure is found at (March 2007)

4. it has not a quarternary structure: only 1 polypeptide chain
HEME
hemoglobin
MYOGLOBIN
it has not a quarternary structure: only 1 polypeptide chain
found in muscles: binds O2 „for storrage“
higher affinity to oxygen than hemoglobin
The figures are found at and (March 2007)

5. Types of hemoglobin and its subunits
adult hemoglobin: HbA1 = 22 HbA2 = 22 ( 2% from total Hb of adults)
fetal hemoglobin HbF = 2 ! higher affinity to O2 than HbA !
binds oxygen more firmly at lower pO2 (placenta!)

6. The figure is found at http://www. labcorp
The figure is found at (March 2007)

7. Structure of heme cyclic tetrapyrrole
the pyrrols has different substituents
belongs among porphyrins (heme = Fe-protoporphyrine IX)
it contains:
conjugated double bonds → red color
4 nitrogen atoms (N)
1 ferrous ion (Fe2+) → in the middle of the tetrapyrrole structure by coordination-covalent bonds

8. Pyrrole
hemoglobin
The figures are found at and (March 2007)

9. Pyrrole
The figures are found at and (March 2007)

10. 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 – 162 g/l
male 135 – 172 g/l

12. 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)
sideropenic anemia – insufficient concentration of Fe
sickle cell anemia – point mutation in the -globin gene forms abnormal HbS (Glu → Val)

13. Synthesis of heme - REPETITION
mainly in the bone marrow (Hb) and in the liver (cytochroms)
mitochondria / cytoplasm / mitochondria
substrates: succinyl-CoA + glycine
important intermediates:
-aminolevulinic acid (= 5-aminolevulinic, ALA)
porphobilinogen (PBG = pyrrol derivative)
uroporphyrinogen III (= 1st porphyrinogen – precursor of heme)
protophorphyrine IX (= direct precursor of heme)

14. The figure is from: Color Atlas of Biochemistry / J. Koolman, K. H
The figure is from: Color Atlas of Biochemistry / J. Koolman, K.H.Röhm. Thieme ISBN

15. Synthesis of heme - regulation
ALA-synthase
the key regulatory enzyme in all tissues
pyridoxal phosphate dependent
ALA-synthase 1 (liver)
inhibited by heme (feed back inhibition)
regulation of transcription and by allosteric mechanism
some drugs  amount of ALA-synthase ( conc. of heme)
ALA-synthase 2 (erythroblasts)
neither feed back inhibition nor induction by drugs
regulated on the level of iron availability

16. Disorders of heme synthesis
PORPHYRIAS
inborn or acquired
classification by defect enzyme
accumulation of heme precursors in the body (skin) and their excretion with urine or feaces (dark color)
neurogical symptomps, photosensitivity
lead poisoning – accumulation of ALA (blood, urine) (inhibition of porphobilinogen synthase)

17. Degradation of hemoglobin
cells of reticulo-endothelial system (RES) of spleen, bone marrow, liver, and skin
Hb released from erythrocytes in blood vesels is bound by haptoglobin → RES
free heme is transported by hemopexin
HEMOGLOBIN → 4x globin + 4x heme
globins chains → amino acids
heme → Fe3+ + CO + biliverdin→bile pigments→feaces

18. The figure is from: Color Atlas of Biochemistry / J. Koolman, K. H
The figure is from: Color Atlas of Biochemistry / J. Koolman, K.H.Röhm. Thieme ISBN

19. Transport of blood gases
Air composition:
78% N2 21% O2 1% water, inert gases, CO2 (0,04%)
Air pressure:
1 atm = Pa (~ 101 kPa) = 760 Torr (= mmHg)
1 mmHg = 0,1333 kPa
1 kPa = 7,5 mmHg

20. 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)

21. The figure is found at http://people. eku
The figure is found at (March 2007)

22. 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

23. 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 disolved (~ 7%)

24. The figure is found at http://fig. cox. miami
The figure is found at (March 2007)

25. Transport of blood gases - reactions in erytrocytes -
tissues:
CO2 + H2O → H2CO3 → HCO3- + H+
H+ + HbO2 → HHb + O2 → aerobic metabolism
lungs:
HHb + O2 → HbO2 + H+
H+ + HCO3- → H2CO3 → H2O + CO2 → excreted

26. O2 O2
The figure is from (March 07)

27. Hemoglobin saturation curve - saturation with oxygen -
The figure is found at (March 2007)

28. The figure is found at http://dr-amy. com/rich/oxygen/fig1
The figure is found at (March 2007)

29. The figure is found at http://dr-amy. com/rich/oxygen/fig1
The figure is found at (March 2007)

30. HbF is left-shifted (it has higher affinity to oxygen)
The figure is found at (March 2007)

31. 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
Hb + O2  HbO2

32. The figure is found at http://employees. csbsju
The figure is found at (March 2007)

33. The animation is found at http://en. wikipedia
The animation is found at (March 2007)

34. 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

35. Bohr´s effect = the saturation of Hb by O2 drops because lowering pH
The figure is found at (March 2007)

36. The figure is found at http://www. nd. edu/~aseriann/dpg
The figure is found at (March 2007)

37. 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
carbonylhemoglobin (over 2%) COHb
after CO poisoning
sulfhemoglobin, cyanhemoglobin
poisoning by H2S, HCN or by cyanides

38. 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)

39. to Fe2+ instead of oxygen
CO binds
to Fe2+ instead of oxygen
The figure is found at (March 2007)

40. The figure is found at http://dr-amy. com/rich/oxygen/fig1
The figure is found at (March 2007)

41. Carbon monoxide poisoning
may result due to:
exposure to automobile exhaust
smoke inhalation
an improperly ventilated gas heater
or other appliance (incomplete burning)

42. Carbon monoxide poisoning
CONSEQUENCES
decreased oxygen-carrying capacity of Hb
decreased delivery of oxygen to cells
CO prevents reversible displacement of O2 on Hb
CO shifts the O2-hemoglobin dissociation curve to the left
CO inhibits the intracellular respiration
CO may bind directly to cardiac and skeletal muscle to cause direct toxicity and to components of the nervous system to cause demyelination and neurologic symptoms

43. „cherry red coloration to the skin“
The figure is found at (March 2007)

44. Saturation of hemoglobin with CO
COHb / total Hb (ratio in %)
Saturation of hemoglobin with CO
physiological value:
 2%
The figure is found at (March 2007)

45. The figure is from http://www. coheadquarters. com/CORisk/figco32x
The figure is from (March 2007)

46. 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