206
5 Plasma Proteins, Yolk Proteins and Metal-Binding Proteins
at least six such proteins in humans which have
been given the names, for example, lipocortin,
placental anticoagulant protein (PAP) or vascular
anticoagulant (VAC) [100]. Finally, reference
must be made to the clotting-regulating components of the thrombin inhibitor AT-III, which has
about the same size (of 60 kDa) in all vertebrates
from the mammals to the amphibians; the human
protein is 423 amino acids long. The clotting inhibitory effect of the polysaccharide heparin is
based on its binding to AT-III, although the affinity of different heparin fractions varies by ten-fold
[23, 284]. Various types of clotting inhibitor are
found in the blood-sucking Hirudinae. The best
known is hirudin from Hirudo medicinalis; this is
a thrombin inhibitor of 65 amino acids (p.101).
Antistasin from Haementeria officinalis (with
119 amino acids) and a similar factor from H. ghilianii have factor Xa-inhibiting activity, and
hementin from H. ghilianii is fibrinolytic. Decorsin (39 amino acids) from the North American
leech Macrobdella decora inhibits aggregation of
the thrombocytes [227].
5.8.2 Blood Clotting in Arthropods
The clotting capacity of arthropod blood varies
considerably according to the species, the developmental stage and the physiological state: it ranges from the complete absence of plasma clotting
to the formation of blood clots whose strength
exceeds those of mammals. For a long time there
was controversy about whether the proteins analogous to fibrinogen (coagulogens) originated in
blood cells or were always to be found dissolved
in the plasma; however, there was no doubt that
the clotting enzyme was of cellular origin. It
would now appear that the arthropods demonstrate all possibilities for the origin of coagulogen: in the xiphosurans they arise only from
blood cells, in the crustaceans only from the haemolymph, whilst in the insects both cellular and
extracellular proteins appear to be involved.
A haemocyte lysate from the xiphosuran
Limulus polyphemus is converted into a gel upon
contact with small amounts of bacterial endotoxins (lipopolysaccharide, LPS). The sensitivity of
this test is so high that it is used in pharmacology
for endotoxin detection [267]. The clotting system
includes the coagulogen and three serine proteases. LPS activates factor C; the activated factor C converts factor B into its active form, which
in turn promotes the conversion of pro-clotting
enzyme to clotting enzyme [180, 256]. The coagulogens from the blood cells of the three species
Limulus polyphemus (North and Central America), Tachypleus tridentatus and Carcinoscorpius
rotundicauda (Southeast Asia) have been
sequenced directly and that of Limulus has been
sequenced via the cDNA. They are polypeptides
of 20 kDa with 175 amino acids, including 16 cysteine residues, and in the case of Limulus and
Tachypleus show 69 % similarity. The clotting
enzyme cleaves the arginyl bonds at 18-Arg and
46-Arg; of the three chains that are thereby created, A (1-18) and B (47-175) form the coagulate, whilst C (19-46) is removed [43, 239]. Factor C is a dimeric glycoprotein made up of a
heavy (80 kDa) chain and a light (43 kDa) chain.
During activation by LPS, the light chain is split
into an A-chain of 8.5 kDa and a B-chain of
34 kDa; the latter contains the catalytic centre.
This arises by cleavage of the bond 72-Phe173-Ile,
which constitutes a difference between the xiphosuran system and the serine proteases of blood
clotting, fibrinolysis and the complement cascade
in mammals, where activation is by cleavage of an
Arg-IleNal bond. There is apparently no other
proteolytic enzyme involved in the activation
reaction of the xiphosurans, but the reaction
mechanism requires further investigation. The Achain has some similarity in a part of its 72amino-acid sequence to several mammalian complement components [180, 256]. The clotting
enzyme is a serine protease of 150 kDa and is present in the blood cells as a zymogen. The haemocytes of Limulus and Tachypleus contain an inhibitor of LPS-dependent clotting. This anti-LPS factor is a polypeptide of 102 amino acids and, surprisingly, has significant homology (22 % ) to rabbit
a-lactalbumin [1].
According to Tait (1911), the crustaceans can
be subdivided into three groups based upon their
clotting type. In group A (e.g. Cancer and Maja)
there is only cell aggregation; in group B (e.g.
Macropipus, Carcinus, Galathea, Homarus)
plasma clotting follows cell aggregation; and in
group C (e.g. Astacus, Panulirus) the solidification of the plasma spreads out from "explosive"
blood cells. However, coagulogens can be purified from the haemolymph of representatives of
all eight genera mentioned, and clot with a haemocyte extract from Macropipus puber. Thus, the
variation between the three groups concerns only
differences in the concentration of the coagulogens [85]. The coagulogens of these eight genera
appear to be structurally quite similar as they all
react with the same clotting enzyme. The coagulogen of the spiny lobster Panulirus interruptus is
5 Plasma Proteins, Yolk Proteins and Metal-Binding Proteins
at least six such proteins in humans which have
been given the names, for example, lipocortin,
placental anticoagulant protein (PAP) or vascular
anticoagulant (VAC) [100]. Finally, reference
must be made to the clotting-regulating components of the thrombin inhibitor AT-III, which has
about the same size (of 60 kDa) in all vertebrates
from the mammals to the amphibians; the human
protein is 423 amino acids long. The clotting inhibitory effect of the polysaccharide heparin is
based on its binding to AT-III, although the affinity of different heparin fractions varies by ten-fold
[23, 284]. Various types of clotting inhibitor are
found in the blood-sucking Hirudinae. The best
known is hirudin from Hirudo medicinalis; this is
a thrombin inhibitor of 65 amino acids (p.101).
Antistasin from Haementeria officinalis (with
119 amino acids) and a similar factor from H. ghilianii have factor Xa-inhibiting activity, and
hementin from H. ghilianii is fibrinolytic. Decorsin (39 amino acids) from the North American
leech Macrobdella decora inhibits aggregation of
the thrombocytes [227].
5.8.2 Blood Clotting in Arthropods
The clotting capacity of arthropod blood varies
considerably according to the species, the developmental stage and the physiological state: it ranges from the complete absence of plasma clotting
to the formation of blood clots whose strength
exceeds those of mammals. For a long time there
was controversy about whether the proteins analogous to fibrinogen (coagulogens) originated in
blood cells or were always to be found dissolved
in the plasma; however, there was no doubt that
the clotting enzyme was of cellular origin. It
would now appear that the arthropods demonstrate all possibilities for the origin of coagulogen: in the xiphosurans they arise only from
blood cells, in the crustaceans only from the haemolymph, whilst in the insects both cellular and
extracellular proteins appear to be involved.
A haemocyte lysate from the xiphosuran
Limulus polyphemus is converted into a gel upon
contact with small amounts of bacterial endotoxins (lipopolysaccharide, LPS). The sensitivity of
this test is so high that it is used in pharmacology
for endotoxin detection [267]. The clotting system
includes the coagulogen and three serine proteases. LPS activates factor C; the activated factor C converts factor B into its active form, which
in turn promotes the conversion of pro-clotting
enzyme to clotting enzyme [180, 256]. The coagulogens from the blood cells of the three species
Limulus polyphemus (North and Central America), Tachypleus tridentatus and Carcinoscorpius
rotundicauda (Southeast Asia) have been
sequenced directly and that of Limulus has been
sequenced via the cDNA. They are polypeptides
of 20 kDa with 175 amino acids, including 16 cysteine residues, and in the case of Limulus and
Tachypleus show 69 % similarity. The clotting
enzyme cleaves the arginyl bonds at 18-Arg and
46-Arg; of the three chains that are thereby created, A (1-18) and B (47-175) form the coagulate, whilst C (19-46) is removed [43, 239]. Factor C is a dimeric glycoprotein made up of a
heavy (80 kDa) chain and a light (43 kDa) chain.
During activation by LPS, the light chain is split
into an A-chain of 8.5 kDa and a B-chain of
34 kDa; the latter contains the catalytic centre.
This arises by cleavage of the bond 72-Phe173-Ile,
which constitutes a difference between the xiphosuran system and the serine proteases of blood
clotting, fibrinolysis and the complement cascade
in mammals, where activation is by cleavage of an
Arg-IleNal bond. There is apparently no other
proteolytic enzyme involved in the activation
reaction of the xiphosurans, but the reaction
mechanism requires further investigation. The Achain has some similarity in a part of its 72amino-acid sequence to several mammalian complement components [180, 256]. The clotting
enzyme is a serine protease of 150 kDa and is present in the blood cells as a zymogen. The haemocytes of Limulus and Tachypleus contain an inhibitor of LPS-dependent clotting. This anti-LPS factor is a polypeptide of 102 amino acids and, surprisingly, has significant homology (22 % ) to rabbit
a-lactalbumin [1].
According to Tait (1911), the crustaceans can
be subdivided into three groups based upon their
clotting type. In group A (e.g. Cancer and Maja)
there is only cell aggregation; in group B (e.g.
Macropipus, Carcinus, Galathea, Homarus)
plasma clotting follows cell aggregation; and in
group C (e.g. Astacus, Panulirus) the solidification of the plasma spreads out from "explosive"
blood cells. However, coagulogens can be purified from the haemolymph of representatives of
all eight genera mentioned, and clot with a haemocyte extract from Macropipus puber. Thus, the
variation between the three groups concerns only
differences in the concentration of the coagulogens [85]. The coagulogens of these eight genera
appear to be structurally quite similar as they all
react with the same clotting enzyme. The coagulogen of the spiny lobster Panulirus interruptus is