6. PROPERTIES OF FISH HEMOGLOBINS
231
of pH, 6.5-7.5. These apparent pK changes are much larger than those
found for human hemoglobin.
Lamprey hemoglobin has a very unusual Bohr effect. Wyman (1964)
points out that the Bohr effect curve is so steep relative to its amplitude
that it cannot be fitted with any choice of independent oxygen-linked
acid groups. It must be postulated that stabilizing interactions exist such
that ionization or protonation of one group facilitates that of another
group. Since this process involves changes in aggregation, it appears
quite possible that the groups involved are at or near the points of
contact between the subunits. The process might be imagined to be
analogous to a zipperlike opening: dissociation into subunits is simultaneously associated with changes in pK values of several acid groups.
The enormous change in oxygen binding below pH 6.5, present in
many teleost fish, was first observed by Root (1931) who observed that
CO, drastically lowered the oxygen saturation of fish bloods at acid pH.
This was regarded as an effect on the oxygen capacity as distinct from
the oxygen affinity, because oxygen capacity was defined as the amount
bound at atmospheric pressure ( ~ 1 5 2
mm p o 2 ) . Oxygen pressures as
high as 1 atm were used in subsequent work (Green and Root, 1933).
This resulted in increased oxygen binding except in the most acid solutions where methemoglobin formed readily. Root and Irving (1941)
found that acidified blood from the tautog, Tuutogu onitis, could be
saturated with CO although it was incapable of becoming saturated with
oxygen at 150mm po2. Scholander and van Dam (1957) considered
whether the Root effect might play a role in the secretion of gases into
the swim bladder and whether sufficiently high oxygen pressures would
be effective in achieving saturation. They used oxygen pressures as high
as 140 atm, but the substantial oxidative effects of such pressures were
not investigated. Their results showed that a Root effect was present in
some fish bloods at pressures of 140 atm but not in other fish which
were sensitive to CO, at low oxygen pressures. They concluded that
the Root effect was not the basis for oxygen secretion in deep sea fish.
However, a correlation does exist: the presence of a functioning swim
bladder is often associated with a Root effect in the blood (Fange,
1966 ) .
The results of Hashimoto et ul. ( 1960) indicate that only one of the two
major components of the hemoglobin of the chum salmon is characterized by a Root effect; the other component is not affected by pH at all.
Detailed studies of the Root effect in carp hemoglobin have been
carried out by Noble et ul. ( 1968, 1969). They found (Fig. 5 ) that carp
hemoglobin is only half-saturated with oxygen when equilibrated with
air at pH 5.6 and 20°C in 0.05 M phosphate, or citrate. The oxygen
231
of pH, 6.5-7.5. These apparent pK changes are much larger than those
found for human hemoglobin.
Lamprey hemoglobin has a very unusual Bohr effect. Wyman (1964)
points out that the Bohr effect curve is so steep relative to its amplitude
that it cannot be fitted with any choice of independent oxygen-linked
acid groups. It must be postulated that stabilizing interactions exist such
that ionization or protonation of one group facilitates that of another
group. Since this process involves changes in aggregation, it appears
quite possible that the groups involved are at or near the points of
contact between the subunits. The process might be imagined to be
analogous to a zipperlike opening: dissociation into subunits is simultaneously associated with changes in pK values of several acid groups.
The enormous change in oxygen binding below pH 6.5, present in
many teleost fish, was first observed by Root (1931) who observed that
CO, drastically lowered the oxygen saturation of fish bloods at acid pH.
This was regarded as an effect on the oxygen capacity as distinct from
the oxygen affinity, because oxygen capacity was defined as the amount
bound at atmospheric pressure ( ~ 1 5 2
mm p o 2 ) . Oxygen pressures as
high as 1 atm were used in subsequent work (Green and Root, 1933).
This resulted in increased oxygen binding except in the most acid solutions where methemoglobin formed readily. Root and Irving (1941)
found that acidified blood from the tautog, Tuutogu onitis, could be
saturated with CO although it was incapable of becoming saturated with
oxygen at 150mm po2. Scholander and van Dam (1957) considered
whether the Root effect might play a role in the secretion of gases into
the swim bladder and whether sufficiently high oxygen pressures would
be effective in achieving saturation. They used oxygen pressures as high
as 140 atm, but the substantial oxidative effects of such pressures were
not investigated. Their results showed that a Root effect was present in
some fish bloods at pressures of 140 atm but not in other fish which
were sensitive to CO, at low oxygen pressures. They concluded that
the Root effect was not the basis for oxygen secretion in deep sea fish.
However, a correlation does exist: the presence of a functioning swim
bladder is often associated with a Root effect in the blood (Fange,
1966 ) .
The results of Hashimoto et ul. ( 1960) indicate that only one of the two
major components of the hemoglobin of the chum salmon is characterized by a Root effect; the other component is not affected by pH at all.
Detailed studies of the Root effect in carp hemoglobin have been
carried out by Noble et ul. ( 1968, 1969). They found (Fig. 5 ) that carp
hemoglobin is only half-saturated with oxygen when equilibrated with
air at pH 5.6 and 20°C in 0.05 M phosphate, or citrate. The oxygen