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BIOLOGY 457/657 PHYSIOLOGY OF MARINE & ESTUARINE ANIMALS

BIOLOGY 457/657 PHYSIOLOGY OF MARINE & ESTUARINE ANIMALS. February 23, 2004 Respiration: Respiratory Pigments. RESPIRATION & METABOLISM. Whole-animal respiration: O 2 consumption (or metabolic rate) of the entire animal

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BIOLOGY 457/657 PHYSIOLOGY OF MARINE & ESTUARINE ANIMALS

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  1. BIOLOGY 457/657PHYSIOLOGY OF MARINE & ESTUARINE ANIMALS February 23, 2004 Respiration: Respiratory Pigments

  2. RESPIRATION & METABOLISM • Whole-animal respiration: O2 consumption (or metabolic rate) of the entire animal • External respiration: Exchange of respiratory gases at the respiratory surface • Internal respiration: Exchange of gases between tissues and circulatory medium • Cellular respiration: Energy metabolism within living cells

  3. GASES IN THE ATMOSPHERE

  4. GASES IN WATER

  5. RESPIRATORY PIGMENTS When respiratory surfaces are more than a few mm from the tissues, a transport system is required for handling respiratory gases. O2 is rather insoluble in water (α = 34.1 ml O2 per liter H2O @ STP (O° C; 101 kPa, 760 torr). Vg = α • (Pg /760) • VH2O In air, PO2 is 21% of 760 mm Hg (760 torr): VO2 = 34.1 • .21 • 1 l H2O = 7.16 ml O2 per l H2O

  6. RESPIRATORY PIGMENTS The minimal solubility of O2 in water (or blood) requires the presence of oxygen-transport systems. Respiratory pigments are specialized protein molecules that reversibly bind oxygen under physiological conditions. These pigments have repeatedly evolved in most animal phyla. The same pigments may be involved in the transport of CO2, or in O2 storage.

  7. RESPIRATORY PIGMENT FUNCTION

  8. CLASSES of RESPIRATORY PIGMENTS Hemoglobin: Consists of an iron/porphyrin (heme) bound to a protein (globin). Is generally polymeric (myoglobin is a monomer); most vertebrate Hb’s are tetrameric (2α and 2β chains; MW = 64kD), and can be very polymeric (MW > 1,000 kD in invertebrate extracellular Hb’s). May occur intracellularly or extracellularly. Phyletic distribution is VERY broad: protozoa, platyhelminths (flatworms), nemerteans (ribbon worms), molluscs, arthropods, echinoderms, annelids, vertebrates.

  9. STRUCTURE OF HEMOGLOBIN

  10. INTRACELLULAR HEMOGLOBINS Advantages of intracellular localization of Hb’s: • Reduction in blood colloidal osmotic pressure. • Reduction in fluid viscosity • Protection from leakage or excretion • Regulation of synthesis and function Question: Why do extracellular hemoglobins have such extremely high molecular weights (> 106 Daltons)?

  11. INVERTEBRATE INTRACELLULAR HEMOGLOBINS (in Annelids)

  12. CHLOROCRUORIN • All are essentially identical to hemoglobins, except for a slight change in the porphyrin molecule. However, this results in the pigment’s being distinctly greenish. • Are all extracellular; MW ~ 3,000 kD. • Occur in a few families of sabellid polychates.

  13. HEMERYTHRIN • Are pink or rosy in color. • Are always intracellular (in nucleated cells); MW ranges from 14 to 100 kD. • Found in a few odd invertebrates (a few polychates, brachiopods, priapulids, sipunculids). • Also contain iron, but the iron atoms are bound directly to amino acid side-chains.

  14. HEMOCYANIN • Uses copper atoms to bind O molecules; has no heme group • Is blue when oxygenated (From Burggren et al. 1993) • Is always extracellular; extremely large and complex (MW 1,000 to 8,000 kD) • Very common: most molluscs, crustaceans, Limulus

  15. OXYGEN TRANSPORT: Oxygen Binding Curves Plot Y (or % saturation) vs PO2 (From Burggren et al. 1993)

  16. Oxygen Binding Curves (2) Y = [oxyprotein]/([oxyprotein] + [deoxyprotein]) The affinity of an oxygen-binding pigment for O2 is commonly given in terms of P50 , the PO2 required to saturate half the binding sites in a population of molecules. Then, Y = PO2 / (PO2 + P50) (From Burggren et al. 1993)

  17. Oxygen Binding Curves (3) Cooperativity: In a polymeric respiratory protein, oxygen binding by one subunit can influence binding by others. This is called cooperativity, symbolized by n. The greater the value of n, the greater the cooperativity. Y = ( PO2 )n / (( PO2 )n + ( P50 )n)

  18. Oxygen Binding Curves (4) In log-log form, this becomes a linear equation, known as the Hillequation (used to determine cooperativity by fitting to real data): log(Y/(1 - Y)) = n (log PO2 - log P50) (From Burggren et al. 1993)

  19. OXYGEN TRANSPORT IN BLOOD (From Burggren et al. 1993)

  20. pH: THE BOHR EFFECT (From Burggren et al. 1993)

  21. pH: THE ROOT EFFECT (From Burggren et al. 1993)

  22. TEMPERATURE EFFECTS (From Burggren et al. 1993)

  23. ORGANIC PHOSPHATE EFFECTS DPG = diphosphoglycerol(From Burggren et al. 1993)

  24. A PHYSIOLOGICAL EXAMPLE from Callinectes sapidus

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