Effects of erythrocytic nucleoside triphosphates on oxygen equilibria of composite and fractionated hemoglobins from the facultative air-breathing amazonian catfish,Hypostomus andPterygoplichthys

1. Oxygen equilibria of Hypostomus and Pterygoplichthys hemoglobins and their sensitivities to the erythrocytic nucleotide triphosphates (NTP), ATP and guanosine triphosphate (GTP) are studied to investigate the mechanisms by which blood adapts to air- and water-breathing (cf. Weber et al. , 1979). 2. Hemoglobins of both species are heterogeneous. All hemoglobin fractions isolated by iso-electric focusing reveal a high sensitivity to NTP, but GTP depresses O 2 affinity about twice as effectively as ATP. A cathodal hemoglobin component with a reversed Bohr effect was found in Pterygoplichthys but not in Hypostomus . 3. The data are discussed in relation to the in vivo cofactor modulation of blood O 2 affinity and the adaptive significance of functional heterogeneity of fish hemoglobins.