02226naa a2200301 a 450000100080000000500110000800800410001910000170006024500980007726000090017552014190018465000120160365000170161565300130163265300370164565300170168265300130169965300150171265300160172770000130174370000150175670000130177170000240178470000160180870000120182470000140183677300740185018101292017-03-30       2000    bl ---       0--  u    #d1 aWEBER, R. E.  aIsohemoglobin differentiation in the bimodal-breathing Amazon catfish Hoplosternum littorale.  c2000  aThe bimodal gill(water)/gut(air)-breeding Amazonian catfish Hoplosternum littorale that frequents hypoxic habitats uses "mammalian" 2,3-diphosphoglycerate (DPG) in addition to "piscine" ATP and GTP as erythrocytic O2 affinity modulators. Its electrophoretically distinct anodic and cathodic hemoglobins (Hb An and Hb Ca) were isolated for functional and molecular characterization. In contrast to Hb An, phosphate-free Hb Ca exhibits a pronunced reverse Boht effect (increased O2 affinity with decreasing pH) that is obliterated by ATP, and opposite pH dependences of Kt (O2 association constant of low affinity, tense state) and the overall heat of oxygenation. Dose-response curves indicate small chloride effects and pronounced and differentiated phosphate effects, DPG &lt ATP &lt GTP &lt IHP. Hb Ca -O2 equilibria analyzed in terms of the Monod-Wyman-Changeux model show that small T state bond energy differences underlie the differentiated phosphate effects. Synthetic peptides, corresponding to N-terminal fragment of the cytoplasmic domain of trout band 3 protein, undergo oxygenation-linked binding to Hb ca, suggesting a metabolic regulatory role for this hemoglobin. The amino acid sequences for the chains of Hb Ca obtained by Edman degradation and cDNA sequencing show unusual substitutions at the phosphate-binding site that are discussed in terms of its reserve Bohr effect and anion sensitivities.  acatfish  aRespiração  aAmazonas  aAmazonian Hoplosternum littorale  aBimodal gill  aBranquia  aPeixe gato  aRespiration1 aFAGO, A.1 aVAL, A. L.1 aBANG, A.1 aHAUWAERT, M. L. van1 aDEWILDE, S.1 aZAL, F.1 aMOENS, L.  tJournal of Biology Chemistrygv.275, n.23, p.17297-17305, June, 2000.