This paper reports the results obtained using the osmotic stress method applied to the purified cathodic and anodic hemoglobins (Hbs) from the catfishHoplosternum littorale, a species that displays facultative accessorial air oxygen-ation. We demonstrate that water potential affects the oxy-gen affinity ofH. littoraleHbs in the presence of an inert solute (sucrose). Oxygen affinity increases when water activity increases, indicating that water molecules stabilize thehigh-affinitystateof theHb.
