Blood Oxygen physically diffused by 0.2ml / 100 ml blood By Hb 20ml / 100ml blood So it’s the main...
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Transcript of Blood Oxygen physically diffused by 0.2ml / 100 ml blood By Hb 20ml / 100ml blood So it’s the main...
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Blood
• Oxygen physically diffused by
• 0.2ml / 100 ml blood
• By Hb 20ml / 100ml blood
• So it’s the main function .
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(Eckert, Fig. 13-1)
Gas transfer system of vertebrates
Low PO2High PO2
High PCO2Low PCO2
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Main functions of blood
• * transport :
• *Oxygen and carbon dioxide » - nutrients» Hormones» Metabolites » Force ( hydraulic )» Temperature
• Immunity
• Coagulation
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Transport of O2 in the blood
Respiratory pigments After O2 diffuses across the respiratory
epithelium it is bound by a respiratory pigment
Respiratory pigments are complexes of proteins and metal ions
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• 1. hemoglobin
• 2. chlorocruorin
• 3. hemerythrin
• 4. hemocyanin
• 5.myoglobin
Which in solution heavy, In cells lighter
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Why Hb inside the cell
• VISCOSITY
• FIGURE 2,1
• CHEMISTRY O2 BINDING
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Chlorocruorin
• Class Polychaeta
• contain Fe
• green in low oxygen, red when saturated
• In solution
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Hemocyanin
• some , molluscs , crustaceans and arachnids
• blue when oxygenated and colorless when deoxygenated
• contain Cu• No porphyrin ring• In solution
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Hemerythrin
• Present in the blood of certain marine invertebrates (e.g. sipunculoid worms, polychaetes)
• Contains iron but not a porphyrin ring • violet-pink when oxygenated, colorless when
deoxygenated• In cells
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Hemoglobin (Hb)
Hemoglobin (Hb)• Increases the carrying capacity of blood for O2
• Four protein (globin) chains, each attached to an iron-containing heme group
• Each heme group consists of a porphyrin ring with an iron atom in the center
• In humans, there are forms of globin: , , in adults (2, 2)
• Form dimers 1 1 2 2
• each Subunits bonded to other by links ( hydrogen ,…)
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• Fe bind to the 4 N with coordinate covalent bond
( the bond e pair is formally contributed by only of the atoms forming the bonds)
• The fifth is his residue from globin • The sixth is oxygen if exist • To give oxyhemoglobin • Each hb can carry 4 o• Subunit interactions altered when Hb binds to
O2 or to other molecules
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(Silverthorn, Fig. 16-7)
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• Hemoglobin loads up with oxygen in the lungs, forming oxyhemoglobin.
• As blood passes through the capillaries, some of the oxyhemoglobin releases oxygen and become deoxyhemoglobin.
Hemoglobin
- Carboxyhemoglobin: Hb saturated with CO
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• Partially saturated hemoglobin – when one to three hemes are bound to oxygen
• The rate that hemoglobin binds and releases oxygen is regulated by:
– PO2, temperature, blood pH, PCO2, and the concentration of BPG (an organic chemical)
• These factors ensure adequate delivery of oxygen to tissue cells
Hemoglobin (Hb)
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Hemoglobin
• Fetal hemoglobin:
• gamma chains (not β) w/ higher affinity for O
• (enhance O transfer from mother to fetus)
• Affinity for CO = 200 x’s greater than for O
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• ( No, CO,H2S) poisoning even at low partial pressures
Oxidation of Fe yields 3+ charge - ferric iron
-methemyoglobin ( Met Hb) does NOT bind oxygen.
ON THE SIXTH PART AWATER MOLECULE
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• Normally Fe may be oxidized ( few)
• So what :
• RBCs have a methemoglobin reductase , which convert small amount to – Hb normal.
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Myoglobin
• Mb is a monomeric heme protein• a store oxygen protein facilitate diffusion • - found in skeletal & cardiac muscle• - contain one heme binds one O2• Globin:• - single polypeptide chain; 154• a.a.; 17.2 kD (monomer)• - 8 helicies (label A-H) 20
hemoglobin
141 =α
Β= 146
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Myoglobin
• • Surface: polar; inside: non polar
• • Fe in Mb is Fe2+ - ferrous iron - the form that binds oxygen
• • Oxygen binds as the sixth ligand to Fe
• Higher affinity for O2 than Hb
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Myoglobin
• Oxidation of Fe yields 3+ charge - ferric iron
-metmyoglobin ( MetMb) does NOT bind oxygen
• Cardiac muscle of diving mammals contain higher (8%) amounts of Myoglobin than most mammals (e.g. 0.5% for a dog)
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Who's haven't: Antarctic Icefish body temperature:-1.7oC
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Who's haven't
Antarctic ice fish lack pigment
• low metabolic needs = low metabolism
• high cardiac output, blood volume
• large heart
• O2 solubility 0.3%
• Blood has lower viscosity– Easier to pump
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Vertebrate Hemoglobin
Polypetidechain
Hemegroups
(Fe center)
2X
2X
4 O2/Hb
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How do respiratory pigments work?
• Reversibly Bind O2: heme group• Hb + O2 HbO2
• To work effectively Hb should:
1. Bind O2 at high PO2 (lung, eqn. shifts right)
2. Release O2 at low PO2 (working tissue, eqn. shifts left)
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• Oxygen binding changes the Hb conformation
• – Without oxygen bound, Fe is out of heme plane
• – Oxygen binding pulls the Fe into the heme plane
• Fe pulls its His F8 ligand along with it
• The F helix moves when oxygen binds
• This change means little to Mb,
• but lots to Hb!
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Mechanism of allosteric change
• Heme iron move <= 0.04 nm induces
• conformation change in Hb
• • One alpha-beta pair moves relative to the other
by 15 degrees upon oxygen binding
• • This massive change is induced by movement of Fe by 0.039 nm when oxygen binds
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• Oxy and deoxy form represent 2 different
• conformation states
• - Hb binds O2 (from T R)
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Cooperativity• Binding 1 O2 “loosens” conformation of Hb
subunits– when “loose”, small changes in PO2 can result in
large changes in saturation
“tight”
“relaxed”
O2
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• Cooperative oxygen binding and release is evident in the dissociation curve for hemoglobin.
• Where the dissociation curve has a steep slope, even a slight change in PO2 causes hemoglobin to load or unload a substantial amount of O2.
• This steep part corresponds to the range of partial pressures found in body tissues.
• Hemoglobin can release an O2 reserve to tissues with high metabolism.
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• Hemoglobin saturation plotted against PO2 produces a oxygen-hemoglobin dissociation curve
• 98% saturated arterial blood contains 20 ml oxygen per 100 ml blood (20 vol %)
• As arterial blood flows through capillaries, 5 ml oxygen are released
Influence of PO2 on Hemoglobin Saturation
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Hb-O2 Dissociation Curve
Desaturated
“tight”
Cooperativity“loose”
Saturation
PO2
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PO2
Fig 42.28
Hb + O2 <--------> HbO2
Fig 42.27
1 1
2
2 (resting tissue)
3 (exercising musc.)
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• Hemoglobin is almost completely saturated at a PO2 of 70 mm Hg
• Further increases in PO2 produce only small increases in oxygen binding
• Oxygen loading and delivery to tissue is adequate when PO2 is below normal levels
Hemoglobin Saturation Curve
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• Only 20–25% of bound oxygen is unloaded during one systemic circulation
• If oxygen levels in tissues drop:– More oxygen dissociates from hemoglobin
and is used by cells – Respiratory rate or cardiac output need not
increase
Hemoglobin Saturation Curve
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Figure 22.7 Respiratory pigments display hyperbolic or sigmoid oxygen equilibrium curves (Part 1)
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Details of Mb-O2 binding
site
Proximal Histidine: coordinated to heme iron