216
AUSTEN RIGGS
caution is needed where a “new” electrophoretically distinct hemoglobin
component is found to be associated with a particular set of ecological
conditions. It must be shown whether the component is really unique
or whether it resulted from the binding of small molecules such as
DPG. This distinction is important because DPG levels do appear
to vary with environmental conditions. For example, a man adapted
to high altitudes has blood with a higher DPG concentration in the
red cells (Lenfant et ul., 1968). It is reasonable to expect similar
phenomena to occur in fish. Effects of hemolysis and dialysis on the
oxygen equilibrium of fish hemoglobins suggest that substances functionally similar to DPG may be present.
Rapoport and Guest (1941) determined the ATP content of the
red cells from three species of teleost [unidentified species of catfish,
the bullhead, Zctulurus (=Ameiurus) melus, and the black bass,
Micropterns dolomieui] . They found 55-70% of the total acid-soluble
phosphorus to be ATP; no phytic acid was found. The ATP content
of dogfish red cells is also substantial (Bricker et al., 1968).
Other complications also occasionally arise to conspire to fool the
unwary. So, for example, molecules of the buffer used in electrophoresis
may form complexes with the protein, and these complexes will migrate
differently from the uncomplexed hemoglobin (Cann and Goad, 1965;
Cann, 1966).
Although some of the reports of multiple hemoglobins in fish may
well result from the presence of allosteric substances, the widespread
occurrence of multiple components with quite different amino acid
compositions and functions suggests that extensive gene duplication
followed by mutation is a major cause of multiplicity. The almost universal occurrence of multiple components in fish, reptiles, and amphibians
but the relative absence from birds and mammals suggests that some
important physiological factor may favor multiplicity and that the
possession of multiple hemoglobins confers an advantage. Is it because
poikilothermic animals are subject to a greater range of environmental
oxygen pressures, and hemoglobins are selected which have appropriately different properties? Or is it because the metabolic rate varies
considerably, and different rates require different hemoglobins? Or
again, do multiple hemoglobins arise because of very little selective
pressure? It may be that it is improtant for certain fish to have a hemoglobin, but not particularly critical what kind of a hemoglobin-any
hemoglobin might do, within rather wide limits. It may be a gratuitous
assumption that every molecular attribute of an animal must be either
advantageous or disadvantageous, that the zero on an “advantage”
scale is always excluded. Be this as it may, some of the fish with
AUSTEN RIGGS
caution is needed where a “new” electrophoretically distinct hemoglobin
component is found to be associated with a particular set of ecological
conditions. It must be shown whether the component is really unique
or whether it resulted from the binding of small molecules such as
DPG. This distinction is important because DPG levels do appear
to vary with environmental conditions. For example, a man adapted
to high altitudes has blood with a higher DPG concentration in the
red cells (Lenfant et ul., 1968). It is reasonable to expect similar
phenomena to occur in fish. Effects of hemolysis and dialysis on the
oxygen equilibrium of fish hemoglobins suggest that substances functionally similar to DPG may be present.
Rapoport and Guest (1941) determined the ATP content of the
red cells from three species of teleost [unidentified species of catfish,
the bullhead, Zctulurus (=Ameiurus) melus, and the black bass,
Micropterns dolomieui] . They found 55-70% of the total acid-soluble
phosphorus to be ATP; no phytic acid was found. The ATP content
of dogfish red cells is also substantial (Bricker et al., 1968).
Other complications also occasionally arise to conspire to fool the
unwary. So, for example, molecules of the buffer used in electrophoresis
may form complexes with the protein, and these complexes will migrate
differently from the uncomplexed hemoglobin (Cann and Goad, 1965;
Cann, 1966).
Although some of the reports of multiple hemoglobins in fish may
well result from the presence of allosteric substances, the widespread
occurrence of multiple components with quite different amino acid
compositions and functions suggests that extensive gene duplication
followed by mutation is a major cause of multiplicity. The almost universal occurrence of multiple components in fish, reptiles, and amphibians
but the relative absence from birds and mammals suggests that some
important physiological factor may favor multiplicity and that the
possession of multiple hemoglobins confers an advantage. Is it because
poikilothermic animals are subject to a greater range of environmental
oxygen pressures, and hemoglobins are selected which have appropriately different properties? Or is it because the metabolic rate varies
considerably, and different rates require different hemoglobins? Or
again, do multiple hemoglobins arise because of very little selective
pressure? It may be that it is improtant for certain fish to have a hemoglobin, but not particularly critical what kind of a hemoglobin-any
hemoglobin might do, within rather wide limits. It may be a gratuitous
assumption that every molecular attribute of an animal must be either
advantageous or disadvantageous, that the zero on an “advantage”
scale is always excluded. Be this as it may, some of the fish with