RESUMO
The five main hemoglobins of the South Brazilian bimodal breathing teleost, Callichthys callichthys were separated, and their oxygenation properties and those of the unfractionated hemolysate were measured at 10, 20 and 30 degrees C. The cathodal Hb component had a higher O2 affinity than the other components and a lower Bohr effect (phi = delta log P 50/delta pH), which is reversed at low and high pH values (6.8 greater than pH greater than 7.8). The other, anodal hemoglobins had normal Bohr effects and similar functional properties. The erythrocytic cofactor ATP had no significant effects on the O2 affinities of the hemolysate and the isolated anodal components at physiological pH conditions, but decreased the affinity of the cathodal Hb over the entire pH range tested (6.5-8.2). All hemoglobins showed high thermal dependence of O2 affinity (delta H values between -62 and -74 kJ mol-1 at pH 8.0), which decreased with falling pH, in accordance with an inverse relation between the Bohr effect and temperature. The possible adaptive significance of the oxygenation patterns of the hemoglobins and their temperature dependences are discussed comparatively with special reference to the closely-related bimodal breather Hoplosternum littorale, and to breathing habit (gill breathing in winter when the fish is a benthic feeder and "gut" air breathing in the warm reproductive season when they nest at the surface).
Assuntos
Peixes/sangue , Hemoglobinas/análise , Animais , Cromatografia por Troca Iônica , Peixes/fisiologia , Brânquias/análise , Concentração de Íons de Hidrogênio , Focalização Isoelétrica , Oxirredução , Respiração , TemperaturaRESUMO
Oxygen equilibria of the multiple hemoglobin (Hb) from the South American cichlid fishes Crenicichla lepidota, Aequidens portalegrensis, and Geophagus brasiliensis were measured at three different temperatures (10, 20 and 30 degrees C). The cofactor-free whole hemolysates exhibited extremely high O2 affinities (half-saturation oxygen tension, P50 approximately 1 mm Hg at pH 7.2 and 20 degrees C), exceptionally large Bohr effects (phi = delta log P50/delta pH = -1.1 to -1.3 at pH 7.2-6.2 and 20 degrees C), low cooperativity, and a low sensitivities to ATP. The O2 affinities showed high thermal sensitivity (delta H for the overall oxygenation reactions were -71 to -79 kJ mol-1 at pH 8.0). Nine Hb components separated from Geophagus showed similar, if not identical, functional properties. The oxygenation properties of the Hb systems, particularly the high thermal and pH sensitivities, are interpreted as adaptions to large diurnal variations in ambient temperature, oxygen tension and activity patterns of the fish in nature.
Assuntos
Peixes/sangue , Hemoglobinas/análise , Animais , Eletroforese das Proteínas Sanguíneas , Concentração de Íons de Hidrogênio , Focalização Isoelétrica , Compostos Organofosforados/metabolismo , Oxirredução , Consumo de Oxigênio , Especificidade da Espécie , TemperaturaRESUMO
Sound planning helps prevent heatstroke, fluid problems, and dysentery, but local practices pose unexpected risks for a baseball team on the move.