548
14 Glycolysis
snail Nassarius coronatus, as in Cardium tuberculatum, produces octopine, and during anoxia produces n-Iactate. The razor shell Ensis directus
produces octopine during activity-dependent
anaerobiosis and strombine during the habitatdependent process [288]. The snail Strombus
luhuanus produces octopine during excessive
muscle activity, mainly strombine during the subsequent recovery period, but alanopine during
anoxia [68, 102].
The cephalopods Sepia officinalis and Loligo
vulgaris possess tissue-specific isoenzymes of
octopine dehydrogenase which resemble the vertebrate LDH isoenzymes in the differences
between their properties and their biological
roles. The enzyme from the brain has higher
affinities for octopine and NAD+ than does the
enzyme from the mantle musculature, and it is
more strongly inhibited by pyruvate and octopine. According to this, the muscle isoenzyme is
preferentially involved in octopine formation and
that from the brain in octopine oxidation. In
agreement with this is the fact that arginine is
released from 14C-Iabelled octopine in the brain
and other organs but not in muscle. The octopine
produced in the mantle muscle during activitydependent anaerobiosis is transported in the haemolymph to other tissues, where it is oxidized
[70]. The bivalves and the gastropod Strombus
luhuanus have only one ODH locus; however,
this is highly polymorphic, e.g. there are eight
alleles in Cardium edule [70]. The two alleloenzymes of ODH in the sea anemone Metridium senile
not only differ in their kinetic properties to the
same extent as the cephalopod isoenzymes, but
also show large frequency differences between
populations. This has been interpreted as adaptation to different living conditions. Three tissuespecific isoenzymes of alan opine dehydrogenase
can be distinguished in the snail Busycotypus
canaliculatum. The enzyme from the hepatopancreas has a high affinity for alanopine; there is
marked product inhibition of alanopine formation but not of its oxidation. In contrast, alanopine production is clearly favoured in the case of
the muscle enzyme, and the enzyme of the gill is
intermediate between these two extremes [191].
14.12 Special Pathways of Anaerobic
Energy Production
14.12.1 Synthesis of Ethanol and Acetic Acid
Ethanol production has been described for acanthocephalans, cestodes, nematodes, some insect
larvae and carp-like fish. In the cyprinids, however, it is found in the crucian carp Carassius
carassius, the goldfish C. auratus and the bitterling Rhodeus amarus but not in the common carp
Cyprinus carpio [276]. None of these species possesses a cytoplasmic pyruvate carboxylase as
occurs in yeast. According to investigations of the
goldfish, the larvae of the non-biting midge Chironomus thummi and the nematode Panagrellus
redivivus, the pyruvate dehydrogenase complex is
responsible for the decarboxylation of pyruvate
to acetaldehyde. The aldehyde is then reduced to
ethanol by NADH-dependent alcohol dehydrogenase. In C. carassius this has its highest activity
in the skeletal muscles and not in the liver, as in
the carp, the rainbow trout Salmo gairdneri and
the rat. On the other hand, the NAD-specific
aldehyde dehydrogenase of the common carp has
a much lower activity in the skeletal muscle than
in the gill, kidney or heart. Probably the most
important function of this enzyme is the oxidation
of aldehyde produced from biogenic amines by a
monoaminooxidase. The musculature of the crucian carp is highly specialized for ethanol production by the high activity of alcohol dehydrogenase
and its separation from the aldehyde dehydrogenase [177]. Other pathways are utilized in the Protozoa. The flagellate Crithidia fasciculata, like
yeast, possesses an ethanol-forming system that
comprises a cytosolic pyruvate decarboxylase and
an alcohol dehydrogenase which mainly reduces
aldehyde [31]. In contrast, Entamoeba histolytica
lacks a pyruvate decarboxylase; in this case,
acetyl-CoA is reduced by an acylating aldehyde
dehydrogenase to acetaldehyde, and further to
ethanol by the NADPH- or NADH-specific alcohol dehydrogenase [141]. Glycerol has been
shown to be the main metabolite of Trichomonas
vaginalis [32].
The rumen ciliates produce acetate, butyrate,
lactate, COz and H2• The metabolism of pyruvate
to acetate and Hz takes place in special cell organelles that are about 0.5 !lm in diameter, the socalled hydrogenosomes, which were found initially in Tritrichomonas foetus and related flagellates. Isotricha species have been found to contain not only all four enzymes involved in the
14 Glycolysis
snail Nassarius coronatus, as in Cardium tuberculatum, produces octopine, and during anoxia produces n-Iactate. The razor shell Ensis directus
produces octopine during activity-dependent
anaerobiosis and strombine during the habitatdependent process [288]. The snail Strombus
luhuanus produces octopine during excessive
muscle activity, mainly strombine during the subsequent recovery period, but alanopine during
anoxia [68, 102].
The cephalopods Sepia officinalis and Loligo
vulgaris possess tissue-specific isoenzymes of
octopine dehydrogenase which resemble the vertebrate LDH isoenzymes in the differences
between their properties and their biological
roles. The enzyme from the brain has higher
affinities for octopine and NAD+ than does the
enzyme from the mantle musculature, and it is
more strongly inhibited by pyruvate and octopine. According to this, the muscle isoenzyme is
preferentially involved in octopine formation and
that from the brain in octopine oxidation. In
agreement with this is the fact that arginine is
released from 14C-Iabelled octopine in the brain
and other organs but not in muscle. The octopine
produced in the mantle muscle during activitydependent anaerobiosis is transported in the haemolymph to other tissues, where it is oxidized
[70]. The bivalves and the gastropod Strombus
luhuanus have only one ODH locus; however,
this is highly polymorphic, e.g. there are eight
alleles in Cardium edule [70]. The two alleloenzymes of ODH in the sea anemone Metridium senile
not only differ in their kinetic properties to the
same extent as the cephalopod isoenzymes, but
also show large frequency differences between
populations. This has been interpreted as adaptation to different living conditions. Three tissuespecific isoenzymes of alan opine dehydrogenase
can be distinguished in the snail Busycotypus
canaliculatum. The enzyme from the hepatopancreas has a high affinity for alanopine; there is
marked product inhibition of alanopine formation but not of its oxidation. In contrast, alanopine production is clearly favoured in the case of
the muscle enzyme, and the enzyme of the gill is
intermediate between these two extremes [191].
14.12 Special Pathways of Anaerobic
Energy Production
14.12.1 Synthesis of Ethanol and Acetic Acid
Ethanol production has been described for acanthocephalans, cestodes, nematodes, some insect
larvae and carp-like fish. In the cyprinids, however, it is found in the crucian carp Carassius
carassius, the goldfish C. auratus and the bitterling Rhodeus amarus but not in the common carp
Cyprinus carpio [276]. None of these species possesses a cytoplasmic pyruvate carboxylase as
occurs in yeast. According to investigations of the
goldfish, the larvae of the non-biting midge Chironomus thummi and the nematode Panagrellus
redivivus, the pyruvate dehydrogenase complex is
responsible for the decarboxylation of pyruvate
to acetaldehyde. The aldehyde is then reduced to
ethanol by NADH-dependent alcohol dehydrogenase. In C. carassius this has its highest activity
in the skeletal muscles and not in the liver, as in
the carp, the rainbow trout Salmo gairdneri and
the rat. On the other hand, the NAD-specific
aldehyde dehydrogenase of the common carp has
a much lower activity in the skeletal muscle than
in the gill, kidney or heart. Probably the most
important function of this enzyme is the oxidation
of aldehyde produced from biogenic amines by a
monoaminooxidase. The musculature of the crucian carp is highly specialized for ethanol production by the high activity of alcohol dehydrogenase
and its separation from the aldehyde dehydrogenase [177]. Other pathways are utilized in the Protozoa. The flagellate Crithidia fasciculata, like
yeast, possesses an ethanol-forming system that
comprises a cytosolic pyruvate decarboxylase and
an alcohol dehydrogenase which mainly reduces
aldehyde [31]. In contrast, Entamoeba histolytica
lacks a pyruvate decarboxylase; in this case,
acetyl-CoA is reduced by an acylating aldehyde
dehydrogenase to acetaldehyde, and further to
ethanol by the NADPH- or NADH-specific alcohol dehydrogenase [141]. Glycerol has been
shown to be the main metabolite of Trichomonas
vaginalis [32].
The rumen ciliates produce acetate, butyrate,
lactate, COz and H2• The metabolism of pyruvate
to acetate and Hz takes place in special cell organelles that are about 0.5 !lm in diameter, the socalled hydrogenosomes, which were found initially in Tritrichomonas foetus and related flagellates. Isotricha species have been found to contain not only all four enzymes involved in the