260
7 Respiratory Pigments
alone in having more IP4 than IPs in its erythrocytes. Avian IPs is 1,3,4,5,6-IPs and the IP4 is always
1,4,5,6-IP4' in contrast to the mammalian isomer
1,3,4,5-IP4 [119]. DPG is present in embryos of
the duck, chicken, pigeon and various other
birds, and is gradually replaced by IPs. The reduction in DPG and ATP in the chicken is related to
the maximum in blood O2 affinity before hatching; this increases the efficiency of O2 transport
through the egg membrane [183].
In most mammalian erythrocytes, DPG is at
such a high concentration (4-12 f,lmollml erythrocytes) that the haemoglobin is unsaturated and its
O2 affinity is reduced two- to threefold. In the
Feloidea and Bovoidea, however, not only is the
haemoglobin organophosphate insensitive but
the DPG concentration in the erythrocytes is
unusually low. During hibernation, e.g. of the
hedgehog, the ground squirrel Spermophilus
mexican us , the marmot and the hamster, the O2
affinity of the blood is increased by a reduction in
erythrocyte DPG concentration [27]. The O2 supply to mammalian foetuses is maintained in various ways. Primates and ruminants produce a special foetal haemoglobin. In the case of the ruminants, this has a high intrinsic O2 affinity and a
reduced DPG sensitivity; furthermore, the amino
acid NAI is missing in the non-u chains and
~NA2-His is replaced by methionine. The foetal
haemoglobins of man and other primates do not
have a higher O2 affinity but do have a lower sensitivity to DPG; in human haemoglobin F, this is
achieved by the presence of serine instead of histidine in position yH21. However, in most mammals, e.g. the dog, horse, pig, guinea-pig, rabbit
and rat there is no special foetal haemoglobin but
simply a lower DPG concentration in foetal
erythrocytes [27].
7.1.4 Temperature Effects and Adaptations
The oxygenation of haemoglobin is usually an
exothermic process; higher temperatures therefore reduce O2 affinity. The enthalpy value (AH)
of oxygenation is extraordinarily variable in the
vertebrates: in the fish it is 0 to -70 kJ/mol O2, in
the reptiles -30 to -50 kJ/mol O2, and in mammals -40 to -60 kJ/mol O2• This is related to the
fact that O2 binding produces heat but the simultaneous T ~ R transition absorbs heat in proportion to the number of broken H bonds. The difference between the two processes is measurable in
terms of the AH value. Organophosphates
reduce the numerical value of AH; because the
binding of organophosphates is exothermic, their
removal during oxygenation requires heat. Thus,
for human haemoglobin AH is -50 kJ/mol O2 in
the absence of DPG and only -30 kllmol O2 in its
presence [75, 183].
Cold-blooded vertebrates show various ways of
preventing a reduction in O2 atrmity with increasing temperature. The first possibility is for several
or all haemoglobins to have AH values close to
zero. This is true, for example, for the haemoglobin of Iguana iguana and Hb I of the rainbow
trout, compaf(~d with AH = -45 kJ/mol O2 for
the Root-effect haemoglobin Hb IV [135]. A corresponding solution is found in fish with a greater
than normal swimming capacity: the arterial
blood, which is cooled in the gills, subsequently
passes through a venous heat-exchanger, where
its temperature is increased by 3-5 °C (in the porbeagle Lamna ditrotus), or even by 15°C in the
tuna Thunnus thynnus, before it reaches the
underlying red musculature. The unavoidable O2
loss by the venous blood is limited by the absence
of a temperature effect on the haemoglobin
(Lamna) or by an inverse temperature effect
(Thunnus), i.e. the O2 affinity remains constant
or increases with an increase in temperature
[131, 132]. The variable temperature sensitivity of
fish haemoglobin apparently does not correlate
with the temperature variability of the environment: haemoglobins with AH values of -60 kJI
mol O2 are found in antarctic species of the genus
Trematomus and in species like Fundulus heteroditus which inhabit regions with extremes of temperature [135]. The heterothermic vertebrates
have a second possibility to reduce the influence
of a temperature change on their haemoglobin:
they can reduce the concentration of organophosphates in the erythrocytes at increasing temperatures. This mechanism is found in, for example,
the turtle Malacochersus tornieri, the frog Rana
esculenta and the fish Ictalurus nebulosus.
7.1.5 The Gene Families of Vertebrate
Haemoglobins
The possession of multiple haemoglobins is the
rule rather than the exception amongst the vertebrates. These are mostly the products of single
genes which are expressed only at certain developmental stages or under particular physiological
conditions.
Allelic
variants
and
posttranslationally altered forms are, however also
widely distributed amongst the haemoglobins.
This variety can be particularly well illustrated in
7 Respiratory Pigments
alone in having more IP4 than IPs in its erythrocytes. Avian IPs is 1,3,4,5,6-IPs and the IP4 is always
1,4,5,6-IP4' in contrast to the mammalian isomer
1,3,4,5-IP4 [119]. DPG is present in embryos of
the duck, chicken, pigeon and various other
birds, and is gradually replaced by IPs. The reduction in DPG and ATP in the chicken is related to
the maximum in blood O2 affinity before hatching; this increases the efficiency of O2 transport
through the egg membrane [183].
In most mammalian erythrocytes, DPG is at
such a high concentration (4-12 f,lmollml erythrocytes) that the haemoglobin is unsaturated and its
O2 affinity is reduced two- to threefold. In the
Feloidea and Bovoidea, however, not only is the
haemoglobin organophosphate insensitive but
the DPG concentration in the erythrocytes is
unusually low. During hibernation, e.g. of the
hedgehog, the ground squirrel Spermophilus
mexican us , the marmot and the hamster, the O2
affinity of the blood is increased by a reduction in
erythrocyte DPG concentration [27]. The O2 supply to mammalian foetuses is maintained in various ways. Primates and ruminants produce a special foetal haemoglobin. In the case of the ruminants, this has a high intrinsic O2 affinity and a
reduced DPG sensitivity; furthermore, the amino
acid NAI is missing in the non-u chains and
~NA2-His is replaced by methionine. The foetal
haemoglobins of man and other primates do not
have a higher O2 affinity but do have a lower sensitivity to DPG; in human haemoglobin F, this is
achieved by the presence of serine instead of histidine in position yH21. However, in most mammals, e.g. the dog, horse, pig, guinea-pig, rabbit
and rat there is no special foetal haemoglobin but
simply a lower DPG concentration in foetal
erythrocytes [27].
7.1.4 Temperature Effects and Adaptations
The oxygenation of haemoglobin is usually an
exothermic process; higher temperatures therefore reduce O2 affinity. The enthalpy value (AH)
of oxygenation is extraordinarily variable in the
vertebrates: in the fish it is 0 to -70 kJ/mol O2, in
the reptiles -30 to -50 kJ/mol O2, and in mammals -40 to -60 kJ/mol O2• This is related to the
fact that O2 binding produces heat but the simultaneous T ~ R transition absorbs heat in proportion to the number of broken H bonds. The difference between the two processes is measurable in
terms of the AH value. Organophosphates
reduce the numerical value of AH; because the
binding of organophosphates is exothermic, their
removal during oxygenation requires heat. Thus,
for human haemoglobin AH is -50 kJ/mol O2 in
the absence of DPG and only -30 kllmol O2 in its
presence [75, 183].
Cold-blooded vertebrates show various ways of
preventing a reduction in O2 atrmity with increasing temperature. The first possibility is for several
or all haemoglobins to have AH values close to
zero. This is true, for example, for the haemoglobin of Iguana iguana and Hb I of the rainbow
trout, compaf(~d with AH = -45 kJ/mol O2 for
the Root-effect haemoglobin Hb IV [135]. A corresponding solution is found in fish with a greater
than normal swimming capacity: the arterial
blood, which is cooled in the gills, subsequently
passes through a venous heat-exchanger, where
its temperature is increased by 3-5 °C (in the porbeagle Lamna ditrotus), or even by 15°C in the
tuna Thunnus thynnus, before it reaches the
underlying red musculature. The unavoidable O2
loss by the venous blood is limited by the absence
of a temperature effect on the haemoglobin
(Lamna) or by an inverse temperature effect
(Thunnus), i.e. the O2 affinity remains constant
or increases with an increase in temperature
[131, 132]. The variable temperature sensitivity of
fish haemoglobin apparently does not correlate
with the temperature variability of the environment: haemoglobins with AH values of -60 kJI
mol O2 are found in antarctic species of the genus
Trematomus and in species like Fundulus heteroditus which inhabit regions with extremes of temperature [135]. The heterothermic vertebrates
have a second possibility to reduce the influence
of a temperature change on their haemoglobin:
they can reduce the concentration of organophosphates in the erythrocytes at increasing temperatures. This mechanism is found in, for example,
the turtle Malacochersus tornieri, the frog Rana
esculenta and the fish Ictalurus nebulosus.
7.1.5 The Gene Families of Vertebrate
Haemoglobins
The possession of multiple haemoglobins is the
rule rather than the exception amongst the vertebrates. These are mostly the products of single
genes which are expressed only at certain developmental stages or under particular physiological
conditions.
Allelic
variants
and
posttranslationally altered forms are, however also
widely distributed amongst the haemoglobins.
This variety can be particularly well illustrated in