6. PROPERTIES OF FISH HEMOGLOBINS
237
Love ( 1963b ) showed, however, that deoxygenated lamprey hemoglobin
is at least partly aggregated and that the oxy form is monomeric. Thus,
the anomalously high n value was found to be associated with an oxygenation-induced dissociation of subunits. This phenomenon is widespread, and it has been found in an abnormal human hemoglobin (Bonaventura and Riggs, 1968) and in many invertebrate hemoglobins (Kitto
and Bonaventura, 1969).
Since dilution favors dissociation into subunits, it might be expected
that n would be concentration dependent. Clearly, sufficient dilution
should result in complete dissociation into monomeric units for which
n should be unity. Briehl’s data for lamprey hemoglobin (Briehl, 1963)
indicate that n increases with degree of oxygenation. Insufficient data
exist to permit an unambiguous conclusion concerning the possible
changes of n with concentration, but no doubt exists about changes
of n with degree of oxygenation. This change is, however, only apparent at oxygenation levels above 50%, and it becomes pronounced only
above 80%. Antonini et al. (1964) have also measured this equilibrium,
but the experiments were apparently confined to the region below 80%;
thus, they did not observe the dependence of n on y . Wyman (1964) has
analyzed the effects of changes in aggregation on the oxygen equilibrium
in some detail. He showed that if the oxygenated molecules are wholly
monomeric and the deoxygenated molecules are all tetramers, the resulting oxygen equilibria will be quite asymmetric with n = 1.6 at the midpoint. The essential feature of Wyman’s model is that a large range
of oxygen pressure exists in which the monomers are 1o!Z oxygenated,
and the tetramers are not oxygenated at all. In this model, the oxygen
equilibria for the tetramers and monomers are each assumed to have
ra = 1. The model predicts a tenfold change in concentration to result
in a change in log P,, of about 0.75, which is not far from that found
by Briehl (1963).
Rumen and Love (1963a) have found that the six components of
Petromyzon marinus hemoglobin differ from one another in their aggregation characteristics. Components 4, 5, and 6 appear to aggregate to
tetramers upon deoxygenation but component 2 does not aggregate at
all and components 1 and 3 display intermediate behavior (Table IV).
Antonini et al. (1964) determined the oxygen equilibrium of each
component (except 2 ) from Petromyson marinus (Table IV) . Components
1 and 4 appear to have significantly different oxygen equilibria from
components 3, 5, and 6. However, these differences may have resulted
from variations in the concentration dependence of the equilibrium
which, in turn, would reflect differences in subunit dissociation equilibria.
In addition, component 1 was reported to be brown even after enzymic
237
Love ( 1963b ) showed, however, that deoxygenated lamprey hemoglobin
is at least partly aggregated and that the oxy form is monomeric. Thus,
the anomalously high n value was found to be associated with an oxygenation-induced dissociation of subunits. This phenomenon is widespread, and it has been found in an abnormal human hemoglobin (Bonaventura and Riggs, 1968) and in many invertebrate hemoglobins (Kitto
and Bonaventura, 1969).
Since dilution favors dissociation into subunits, it might be expected
that n would be concentration dependent. Clearly, sufficient dilution
should result in complete dissociation into monomeric units for which
n should be unity. Briehl’s data for lamprey hemoglobin (Briehl, 1963)
indicate that n increases with degree of oxygenation. Insufficient data
exist to permit an unambiguous conclusion concerning the possible
changes of n with concentration, but no doubt exists about changes
of n with degree of oxygenation. This change is, however, only apparent at oxygenation levels above 50%, and it becomes pronounced only
above 80%. Antonini et al. (1964) have also measured this equilibrium,
but the experiments were apparently confined to the region below 80%;
thus, they did not observe the dependence of n on y . Wyman (1964) has
analyzed the effects of changes in aggregation on the oxygen equilibrium
in some detail. He showed that if the oxygenated molecules are wholly
monomeric and the deoxygenated molecules are all tetramers, the resulting oxygen equilibria will be quite asymmetric with n = 1.6 at the midpoint. The essential feature of Wyman’s model is that a large range
of oxygen pressure exists in which the monomers are 1o!Z oxygenated,
and the tetramers are not oxygenated at all. In this model, the oxygen
equilibria for the tetramers and monomers are each assumed to have
ra = 1. The model predicts a tenfold change in concentration to result
in a change in log P,, of about 0.75, which is not far from that found
by Briehl (1963).
Rumen and Love (1963a) have found that the six components of
Petromyzon marinus hemoglobin differ from one another in their aggregation characteristics. Components 4, 5, and 6 appear to aggregate to
tetramers upon deoxygenation but component 2 does not aggregate at
all and components 1 and 3 display intermediate behavior (Table IV).
Antonini et al. (1964) determined the oxygen equilibrium of each
component (except 2 ) from Petromyson marinus (Table IV) . Components
1 and 4 appear to have significantly different oxygen equilibria from
components 3, 5, and 6. However, these differences may have resulted
from variations in the concentration dependence of the equilibrium
which, in turn, would reflect differences in subunit dissociation equilibria.
In addition, component 1 was reported to be brown even after enzymic