Lecture 16 - Respiratory Pigments PDF

Lecture 15 (10 Oct.): Respiratory Pigments Reading Ch. 24.1-24.3 1 1  Pigments & gas diffusion Gases that combine chemically with other molecules no longer contribute to partial pressure implications for diffusion?...

Lecture 15 (10 Oct.): Respiratory Pigments Reading Ch. 24.1-24.3 1 1  Pigments & gas diffusion Gases that combine chemically with other molecules no longer contribute to partial pressure implications for diffusion? CO2 + H2O  H2CO3  H+ + HCO3- 𝐻𝑏 𝐻 + 𝑂2 ՞ 𝐻𝑏 𝑂2 + 𝐻+ 2 2  O2 Transport: respiratory pigments Heme: porphyrin ring complexed with one iron atom Myoglobin (Mb): monomeric protein (globin) plus one heme molecule – where typically found? 3 3  Pigment diversity Chlorocruorins: use iron and different porphyrin ring from Mb, Hb when bind O2 they turn green four types of marine annelid worms Feather duster worms 4 4  Pigment diversity Hemerythrins: non-porphyrin, iron- containing proteins found within muscle and blood cells some types of worms and brachiopods Sipunculid worm Brachiopod mollusc 5 5  Pigment diversity Hemocyanins : copper containing, non- porphyrin proteins with up to 160 O2 binding sites – when bind O2 they turn blue found extracellularly in some molluscs and arthropods Decapod crustacean (lobster) Cephalopod mollusc (squid) 6 6  Pigment diversity-plants?? Leghemoglobin: monomeric (like Mb), porphyrin ring, globin protein in legumes supplies O2 for symbiotic bacteria, which fix N2 for plant soybean root nodules 7 7  Hemoglobin (Hb) most vertebrate blood cells up to four heme-globin subunits – mammals 2 α, 2 β crocodile icefish 8 8  O2 – Hb binding: Key points 𝐻𝑏 𝐻 + 𝑂2 ՞ 𝐻𝑏 𝑂2 + 𝐻+ 1. equilibrium reaction – higher PO2, more binding – low PO2, O2 unbinds from Hb 2. O2 – binding non-linear (sigmoidal) 3. O2 only available to tissue if unbound 4. binding/unbinding affected by internal environment – acute effects – temp., pH, CO2 etc. 9 9  1: Equilibrium binding – higher PO2, more binding – low PO2, O2 unbinds from Hb – why would PO2 fall in blood – very little O2 dissolved in blood plasma 10 10  2: Binding sigmoidal – cooperativity: binding O2 at one Hb subunit of multimeric facilitates binding at other subunits (slope increases) – at high PO2 most subunits “saturated” (slope decreases) 11 11  3: O2 must unbind to access tissues – at lungs high PO2 so can diffuse into blood, bind to HB – at exercising muscle, blood PO2 low so O2 more likely to unbind from Hb 12 12  Hb vs. Mb – Mb monomeric, so no cooperativity – What happens to O2 as blood passes through a Mb-containing muscle? 13 13  Describing Hb – O2 binding P50: PO2 at which Hb reaches 50% saturation – measure of affinity of Hb for O2 – can change acutely, with acclimation and adaptation 14 14  “Shifting” Hb – O2 binding 15 15  Hb Adaptations: changing amino acid sequence of globin molecule can change P50 16 16  Hb Adaptations: Water vs. Air breathers 17 17  Hb Adaptations: Water vs. Air breathers…why? 18 18  Hb Adaptations: O2 availability animals living in low O2 environments… Wilmer, Stone, Johnston. 2000. Environ. Physiol. of Animals 19 19  Hb Adaptations: High Altitude 20 20  Hb Adaptations: Burrowers 21 21  Hb Adaptations: Body Size Smaller mammals… 22 22  Hb Acclimation: express different globin isoforms in response to changing O2 availability change in P50 (blue line) 23 23  4: Hb – acute binding effects Bohr effect/shift: pH and/or CO2 24 24  4: Hb – acute binding effects temperature 25 25  4: Hb – acute binding effects organic phosphates in blood cells bind to Hb and reduce affinity for O2 Fish: ATP, GTP, Inositol pentaphosphate (IPP) Amphibians: ATP, 2,3- diphosphoglycerate (DPG) some GTP Reptiles: ATP, GTP Birds: DPG (embryo), IPP (adult) Mammals: DPG 26 26  Organophosphate modulators 27 27  Compare Hb at lung vs. working muscle Factor Lung Muscle Favours? PO2? Temperature? CO2/pH 28 28  Hb Quantity increase expression, synthesis of Hb, red blood cells (red line) 29 29  Hb Quantity Hematocrit: % blood volume comprised of red blood cells 30 30  Hematocrit: Adaptation diving animals have higher hematocrit 31 31  Hematocrit: Adaptation diving animals have higher hematocrit higher total O2 carrying capacity 32 32  Hematocrit: Acclimation Acclimation to high altitude can increase hematocrit (if enough dietary iron) 33 33  Mammalian fetal hemoglobin fetus expresses γ globin, incorporates four into Hb – γ globin less sensitive to organophospates? lower P50 than maternal – consequences? 34 34