6. PROPERTIES OF FISH HEMOGLOBINS
235
linked protons and the heats of the buffering groups (tris) in the solution. Tris has a heat of ionization of ~ 1 0 , 0 0 0 cal/mole. If the oxygenlinked groups also have heats of ionization close to this value, the
measured heat of ionization might well be independent of pH. This,
however, does not explain why the heat of oxygenation is also apparently
zero.
E. Adaptations of Hemoglobins in Different Fish
The properties of fish hemoglobins reflect adaptations not only to
the metabolic rate but also to the prevailing external oxygen pressure:
the hemoglobin must not only be capable of combining with oxygen at
the environmental po2, but aIso of unloading the oxygen at pressures
appropriate for the tissue metabolism. The overall pattern is that those
fish (i.e., trout and mackerel) which are most active generally have
hemoglobins with lower affinities for oxygen (high P5,,) than do less
active fish. Furthermore, these hemoglobins usually have the largest
Bohr effects. Thus those fish with the highest oxygen requirements and
the largest C 0 2 production have hemoglobins adapted both to deliver
oxygen at relatively high pressures and to facilitate removal of COz.
Although a large Bohr effect helps release oxygen in the tissues, it can
also prevent adequate binding of oxygen in the gills. Under the stress
of emergency and violent muscular activity the lowered oxygen binding
which results from the increase in lactic acid can be catastrophic, and
it may be one of the major causes of death in hyperactive fish (Black,
1958). The Bohr effect, deemed an advantage under normal circumstances, may thus prevent adequate oxygen from reaching the tissues.
Fish which live in a low oxygen environment, and which lack special
adaptations (lung, mouth, or gut) for air breathing, usually have hemoglobins with high oxygen affinities (low
Pelagic fish live in a relatively constant environment with a high po2 (-100-160 mm) where
the P , . ~ . is usually less than 1 mm. These fish usually have hemoglobins
with relatively low oxygen affinities. Variation of the oxygen transport
propcrties of the bloods of these fish depends primarily on metabolic
requirements. Under environmental conditions which prevent equilibration with the atmosphere, however, the p o l may become relatively high:
this situation occurs under the arctic pack ice (Kelley, 1968). Oxygen
transport propcrties of the hemoglobins of fish living under these circumstances have not been studied, but the total quantity of hemoglobin
in the blood of arctic fishes is frequently considerably reduced; much
more 0, is physically dissolved (Scholander and van Dam, 1957).
Although the oxygen transport properties of bloods are frequently
235
linked protons and the heats of the buffering groups (tris) in the solution. Tris has a heat of ionization of ~ 1 0 , 0 0 0 cal/mole. If the oxygenlinked groups also have heats of ionization close to this value, the
measured heat of ionization might well be independent of pH. This,
however, does not explain why the heat of oxygenation is also apparently
zero.
E. Adaptations of Hemoglobins in Different Fish
The properties of fish hemoglobins reflect adaptations not only to
the metabolic rate but also to the prevailing external oxygen pressure:
the hemoglobin must not only be capable of combining with oxygen at
the environmental po2, but aIso of unloading the oxygen at pressures
appropriate for the tissue metabolism. The overall pattern is that those
fish (i.e., trout and mackerel) which are most active generally have
hemoglobins with lower affinities for oxygen (high P5,,) than do less
active fish. Furthermore, these hemoglobins usually have the largest
Bohr effects. Thus those fish with the highest oxygen requirements and
the largest C 0 2 production have hemoglobins adapted both to deliver
oxygen at relatively high pressures and to facilitate removal of COz.
Although a large Bohr effect helps release oxygen in the tissues, it can
also prevent adequate binding of oxygen in the gills. Under the stress
of emergency and violent muscular activity the lowered oxygen binding
which results from the increase in lactic acid can be catastrophic, and
it may be one of the major causes of death in hyperactive fish (Black,
1958). The Bohr effect, deemed an advantage under normal circumstances, may thus prevent adequate oxygen from reaching the tissues.
Fish which live in a low oxygen environment, and which lack special
adaptations (lung, mouth, or gut) for air breathing, usually have hemoglobins with high oxygen affinities (low
Pelagic fish live in a relatively constant environment with a high po2 (-100-160 mm) where
the P , . ~ . is usually less than 1 mm. These fish usually have hemoglobins
with relatively low oxygen affinities. Variation of the oxygen transport
propcrties of the bloods of these fish depends primarily on metabolic
requirements. Under environmental conditions which prevent equilibration with the atmosphere, however, the p o l may become relatively high:
this situation occurs under the arctic pack ice (Kelley, 1968). Oxygen
transport propcrties of the hemoglobins of fish living under these circumstances have not been studied, but the total quantity of hemoglobin
in the blood of arctic fishes is frequently considerably reduced; much
more 0, is physically dissolved (Scholander and van Dam, 1957).
Although the oxygen transport properties of bloods are frequently