haemoglobins are in general higher than those of
the vertebrate haemoglobins. An (alkaline) Bohr
effect, where it exists, is usually only of weak
intensity. Annelid haemoglobins are able to bind
anions and cations but only the latter influence
structural and functional properties. The affinity
is 1000-fold higher for divalent ions, like Ca2+ and
Mg2+, than for monovalent ions. There are highaffinity binding sites which are always saturated
under physiological conditions and are responsible, above all, for stabilizing contacts between
the 1I12th fragments. There are also Ca 2 + -binding
sites of lower affinity which modulate functional
properties such as O2 affinity and cooperativity
[108]. The haemoglobins of Lumbricus and Tylorrhynchus were found to contain 1-4 tightly bound
copper and zinc atoms in addition to 50-61 calcium atoms [153]. Organophosphates have no
effect on annelid haemoglobins. The temperature
sensitivity appears to be generally low; the AH of
about -25 kJ/mol O2 is lower than for many vertebrate haemoglobins [43].
The structure of pogonophoran haemoglobins
allows conclusions to be drawn about the systematic position of this unique group of animals.
These sedentary worms of the seabed were initially considered to be a unique phylum close to
the Hemichordata on the basis of their three body
subdivisions (archimerie); more recent studies of
intact Pogonophora, however, show the existence
of a fourth, bristle-bearing, segmented region
which was missing in the original specimens. This
morphological similarity to the annelids is parallelled by marked similarities between the haemoglobins.
The giant, tube-inhabiting worms of the genera
Riftia and Lamellibrachia, which are amongst the
characteristic inhabitants of hydrothermal vents,
have recently been divorced from the Pognophora
and placed in a new phylum, the Vestimentifera.
Hydrothermal vents are openings in the seabed
from which hot water with a high hydrogen sulphide content emerges; they were discovered in
1977 at a depth of 2000-3000 m off the Galapagos
Islands. This extreme habitat with temperatures of
6-25 °C, a pH value of about 3.5, and an H2S concentration of over 10 mmolll is occupied by giant,
tube-dwelling worms (Riftia pachyptila) , which
are 1-3 m long and have a diameter of 4-5 cm,
and by large mussels of the species Calyptogena
magnifica, with a diameter of 25-30 cm. Riftia has
no gut but instead has a special organ (trophosome) that hosts chemosynthetic, symbiotic bacteria which oxidize sulphide to sulphate; the energy
extracted in this way is used to convert carbon
7.2.1 Annelids, Pogonophora and Echiurids
269
dioxide to various organic substances. Similar
bacteria are to be found in the gills of the mussel
and also in various deep-sea annelids [74].
Riftia has two haemoglobins in the blood and
coelom fluid; the predominant Hb A form in the
blood has a hexameric structure and a molecular
mass of 1.5 MDa, and the Hb B of the coelom
fluid has a mass of 400 kDa. Both forms have the
capacity to bind SH- ions, whereby the binding
capacity of Hb A (1-2 mol sulphide/mol haem) is
greater than that of Hb B (0.4-1). The haemoglobin here apparently serves to supply the symbiotic
bacteria with SH- ions and to protect the animal
tissues from the highly toxic effect of a high concentration of free sulphide [108]. The second
pogonophoran species with a well-investigated
haemoglobin is Lamellibrachia sp., which lives in
less extreme hydrothermal regions. These species
also possess two haemoglobins with different
molecular masses. The 3-MDa haemoglobin contains two haem-free linker chains, AV and AVI, of
about 30 kDa, and four haem-bearing chains of
about 16 kDa, of which AlII and AIV are present
as monomers and AI and All are associated as a
dimer. The 440-kDa haemoglobin is made up only
of the haem-bearing chains BI-BIY. The Nterminal sequences have been determined for all
eight haem-bearing chains; All agrees with BII,
and AlII with BIll. The complete amino acid
sequences are known for AlII and the linker
chain AV. The chains AI, All, AlII, BII and BIll
all have a free cysteine residue which probably
represents the sulphide-binding site. The haembearing chains of Lamellibrachia are all significantly homologous to those of the annelids and
may be incorporated into the annelid dichotomous phylogenetic tree; AI, BI and AIIIIBIII
belong to the aA group of annelid subunits, and
AIIIIBII, AIV and BIV belong to the bB group.
The AV linker agrees at 27 % of positions with the
homologous subunits of the polychaete Tylorrhynchus heterochaetus [161].
The green chlorocruorins are present in solution in the blood of the sedentary polychaetes of
the families Sabellidae, Serpulidae, Chlorhaemidae and Ampharetidae. The prosthetic group is
spirographis haem, which differs from proto haem
only by having a 2-formyl instead of a 2-vinyl residue (Fig. 7.2). Apart from this, the chlorocruorins are identical to the annelid extracellular haemoglobins in molecular size, electron microscopic
appearance, haem content, and dissociation
kinetics. Even very closely related species differ
simply with respect to these two respiratory pigments, e.g. Spirorbis borealis has chlorocruorin,
the vertebrate haemoglobins. An (alkaline) Bohr
effect, where it exists, is usually only of weak
intensity. Annelid haemoglobins are able to bind
anions and cations but only the latter influence
structural and functional properties. The affinity
is 1000-fold higher for divalent ions, like Ca2+ and
Mg2+, than for monovalent ions. There are highaffinity binding sites which are always saturated
under physiological conditions and are responsible, above all, for stabilizing contacts between
the 1I12th fragments. There are also Ca 2 + -binding
sites of lower affinity which modulate functional
properties such as O2 affinity and cooperativity
[108]. The haemoglobins of Lumbricus and Tylorrhynchus were found to contain 1-4 tightly bound
copper and zinc atoms in addition to 50-61 calcium atoms [153]. Organophosphates have no
effect on annelid haemoglobins. The temperature
sensitivity appears to be generally low; the AH of
about -25 kJ/mol O2 is lower than for many vertebrate haemoglobins [43].
The structure of pogonophoran haemoglobins
allows conclusions to be drawn about the systematic position of this unique group of animals.
These sedentary worms of the seabed were initially considered to be a unique phylum close to
the Hemichordata on the basis of their three body
subdivisions (archimerie); more recent studies of
intact Pogonophora, however, show the existence
of a fourth, bristle-bearing, segmented region
which was missing in the original specimens. This
morphological similarity to the annelids is parallelled by marked similarities between the haemoglobins.
The giant, tube-inhabiting worms of the genera
Riftia and Lamellibrachia, which are amongst the
characteristic inhabitants of hydrothermal vents,
have recently been divorced from the Pognophora
and placed in a new phylum, the Vestimentifera.
Hydrothermal vents are openings in the seabed
from which hot water with a high hydrogen sulphide content emerges; they were discovered in
1977 at a depth of 2000-3000 m off the Galapagos
Islands. This extreme habitat with temperatures of
6-25 °C, a pH value of about 3.5, and an H2S concentration of over 10 mmolll is occupied by giant,
tube-dwelling worms (Riftia pachyptila) , which
are 1-3 m long and have a diameter of 4-5 cm,
and by large mussels of the species Calyptogena
magnifica, with a diameter of 25-30 cm. Riftia has
no gut but instead has a special organ (trophosome) that hosts chemosynthetic, symbiotic bacteria which oxidize sulphide to sulphate; the energy
extracted in this way is used to convert carbon
7.2.1 Annelids, Pogonophora and Echiurids
269
dioxide to various organic substances. Similar
bacteria are to be found in the gills of the mussel
and also in various deep-sea annelids [74].
Riftia has two haemoglobins in the blood and
coelom fluid; the predominant Hb A form in the
blood has a hexameric structure and a molecular
mass of 1.5 MDa, and the Hb B of the coelom
fluid has a mass of 400 kDa. Both forms have the
capacity to bind SH- ions, whereby the binding
capacity of Hb A (1-2 mol sulphide/mol haem) is
greater than that of Hb B (0.4-1). The haemoglobin here apparently serves to supply the symbiotic
bacteria with SH- ions and to protect the animal
tissues from the highly toxic effect of a high concentration of free sulphide [108]. The second
pogonophoran species with a well-investigated
haemoglobin is Lamellibrachia sp., which lives in
less extreme hydrothermal regions. These species
also possess two haemoglobins with different
molecular masses. The 3-MDa haemoglobin contains two haem-free linker chains, AV and AVI, of
about 30 kDa, and four haem-bearing chains of
about 16 kDa, of which AlII and AIV are present
as monomers and AI and All are associated as a
dimer. The 440-kDa haemoglobin is made up only
of the haem-bearing chains BI-BIY. The Nterminal sequences have been determined for all
eight haem-bearing chains; All agrees with BII,
and AlII with BIll. The complete amino acid
sequences are known for AlII and the linker
chain AV. The chains AI, All, AlII, BII and BIll
all have a free cysteine residue which probably
represents the sulphide-binding site. The haembearing chains of Lamellibrachia are all significantly homologous to those of the annelids and
may be incorporated into the annelid dichotomous phylogenetic tree; AI, BI and AIIIIBIII
belong to the aA group of annelid subunits, and
AIIIIBII, AIV and BIV belong to the bB group.
The AV linker agrees at 27 % of positions with the
homologous subunits of the polychaete Tylorrhynchus heterochaetus [161].
The green chlorocruorins are present in solution in the blood of the sedentary polychaetes of
the families Sabellidae, Serpulidae, Chlorhaemidae and Ampharetidae. The prosthetic group is
spirographis haem, which differs from proto haem
only by having a 2-formyl instead of a 2-vinyl residue (Fig. 7.2). Apart from this, the chlorocruorins are identical to the annelid extracellular haemoglobins in molecular size, electron microscopic
appearance, haem content, and dissociation
kinetics. Even very closely related species differ
simply with respect to these two respiratory pigments, e.g. Spirorbis borealis has chlorocruorin,