liver a greater amount of oxygen than it would have if the curve had been pH insensitive (see Fig. 1).While the pH sensitivity of human hemoglobin certainly plays an important role in respiration, its magnitude is dwarfed in comparison to the profound changes brought onto some fish hemoglobins by H+ions (5). Y
0.~1 /
1
Fish Hemoglobins Fishes in general have several hemoglobins (12-15). Some function as carriers of oxygen for respiratory purposes much like the human hemoglobin. Others display a strong pH sensi0.0 tivity, and the fish relies on them to inflate its 1 .O 1.5 2.0 2.5 3.0 bladder. The oxygenation curve of one such hemoglobin from the trout Salmo irideus is l o g Po,(mm Hg) shown in Figure 2. In well- aerated waters where the trout lives, Po* is 150 mm Hg and Figure 2. Oxygenation curve of the trout Salmo irideus hemoglobin. The curves are for the hemoglobin at the gills is over 90% satu- Hb IV, one of the several hemoglobins present in the trout. When extrapolated to higher this hemoglobinenters the capil- pressures. the curve for pH = 6.3 indicates that the trout hemoglobin becomes 90% rated, men lary mesh of the bladder, where the pH is saturated at log Po? 4-- an oxygen pressure of about 1.5atm.
lower, the fractional saturation drops. How far the drop is depends on the PoSin
