highly specific. Between these two are enzymes
that metabolize alanine and glycine, and these
are better described as alanopine/strombine
dehydrogenases, e.g. from the mussels Crassostrea gigas, Mytilus edulis and Mercenaria mercenaria and from the polychaete Arenicola marina
[190, 242]. The tauropine dehydrogenases are
also active with alanine [69]. All opine dehydrogenases are stereo-specific. Of all possible
octopine isomers, only N-(S)-I-carboxy-4-guanidinobutyl-(R)-alanine occurs naturally; mesoalanopine arises from alanine. The enzymes from
Halichondria panicea and Crassostrea gigas are
only active against N-carboxymenthyl-(R)alanine and not against the (S)- isomer [70].
Critical for the regulation of opine debydrogenases is the fact that the affinity for one of the
substrates is positively influenced by the other
two. Thus, for example, the affinity of the ODHs
of sea anemones and cephalopods for arginine
and pyruvate is increased by NADH. Similarly,
alanine enhances the pyruvate affinity of the alanopine dehydrogenase of Littorina littorea and
vice versa. The affinity of the Littorina enzyme
for alanine and pyruvate is also increased by a
decrease in pH, and in this way alanopine production is stimulated by the anoxia-related acidosis
[190]. A marked product inhibition is typical of
most opine dehydrogenases, e.g. the effect of
octopine on the ODH of sea anemones and
cephalopods, and the effect of alanopine on the
enzyme of the polychaete Aphrodite aculeata
[70, 242]. Allosteric inhibition by ATP, ADP and
AMP has been reported for the alanopine dehydrogenase of the oyster Crassostrea gigas.
The biological role of the different pyruvate
reductases is by no means always obvious. For
example, both the sea anemones and the cockle
Cardium edule possess an ODH but do not produce octopine [155]. Opine dehydrogenases are
usually found together with LDH, and a not
insignificant number of species contain more than
one type of opine dehydrogenase; the relative
proportions of the individual pyruvate reductases
vary from tissue to tissue [70]. The species- and
organ-specific spectrum of the pyruvate reductases and the differences in their substrate specificity and kinetic-regulatory properties can probably
be looked upon as adaptations to the speciesspecific spectrum of free amino acids or the different physiological functions of the enzymes. In the
polychaete Aphrodite aculeata, each tissue contains only one opine dehydrogenase: longitudinal
muscles, nervous tissue and scales have a broadspecificity alanopine dehydrogenase and the gut
14.11.3 Opine Dehydrogenases
547
has a highly specific strombine dehydrogenase;
LDH and ODH are both absent [242]. The snail
Busycotypus canaliculatum possesses alan opine
dehydrogenase, ODH and LDH. Alanopine
dehydrogenases are to be found in all the organs
and are important especially during habitatdependent anaerobiosis; ODH occurs mainly in
the muscle, and links phosphagen cleavage and
glycolysis during activity-dependent anaerobiosis; LDH is restricted to the heart ventricle and
the continuously active proboscis muscle [191]. In
the edible mussel Mytilus edulis, the opine dehydrogenase of the gut is alanine specific, whereas
the muscle enzyme, which has a particularly high
glycine concentration, can also efficiently metabolize glycine [190].
Many animals possess different pyruvate
reductases that are active in different physiological situations [84] (Table 14.5). This is of biological advantage when both hypoxic conditions
and the need to escape predators occur in the life
of an animal. The presence of multiple pyruvate
reductases ensures that the products formed in
one reaction do not inhibit the enzymes of the
other reactions [70]. Cardium tubercula tum has
altogether aD-specific LDH, two ODHs, four
alanopine dehydrogenases and a strombine
dehydrogenase. However, activity-dependent
anaerobiosis gives rise exclusively to octopine,
whereas habitat-dependent anaerobiosis produces mainly D-Iactate (in addition to alanine) but
only a little octopine, very little alanopine and no
strombine. This ratio of end products is in accordance with the kinetic-regulatory properties of the
enzymes and the intracellular concentrations of
substrates and co substrates [156].
For the alanopine/strombine dehydrogenase of
Arenicola marina, the ratio of the activities
against alanine and glycine shifts with decreasing
NADH concentration in favour of the latter, so
that during activity-dependent anaerobiosis with
a high rate of glycolysis mainly alanopine is produced, and in habitat-dependent anaerobiosis
with reduced metabolism mainly strombine is
produced, in addition to succinate, propionate
and alanine [231]. Sipunculus nudus produces
mainly octopine during activity-dependent anaerobiosis but strombine during anoxia. However,
the octopine/strombine dualism is not fully
explained by the kinetic properties of ODH and
strombine/alanopine dehydrogenase and by the
concentrations of the substrates and cosubstrates.
There are further cases in which the adjustments
in metabolism are not completely understood:
The activity of the pedal retractor muscle of the
that metabolize alanine and glycine, and these
are better described as alanopine/strombine
dehydrogenases, e.g. from the mussels Crassostrea gigas, Mytilus edulis and Mercenaria mercenaria and from the polychaete Arenicola marina
[190, 242]. The tauropine dehydrogenases are
also active with alanine [69]. All opine dehydrogenases are stereo-specific. Of all possible
octopine isomers, only N-(S)-I-carboxy-4-guanidinobutyl-(R)-alanine occurs naturally; mesoalanopine arises from alanine. The enzymes from
Halichondria panicea and Crassostrea gigas are
only active against N-carboxymenthyl-(R)alanine and not against the (S)- isomer [70].
Critical for the regulation of opine debydrogenases is the fact that the affinity for one of the
substrates is positively influenced by the other
two. Thus, for example, the affinity of the ODHs
of sea anemones and cephalopods for arginine
and pyruvate is increased by NADH. Similarly,
alanine enhances the pyruvate affinity of the alanopine dehydrogenase of Littorina littorea and
vice versa. The affinity of the Littorina enzyme
for alanine and pyruvate is also increased by a
decrease in pH, and in this way alanopine production is stimulated by the anoxia-related acidosis
[190]. A marked product inhibition is typical of
most opine dehydrogenases, e.g. the effect of
octopine on the ODH of sea anemones and
cephalopods, and the effect of alanopine on the
enzyme of the polychaete Aphrodite aculeata
[70, 242]. Allosteric inhibition by ATP, ADP and
AMP has been reported for the alanopine dehydrogenase of the oyster Crassostrea gigas.
The biological role of the different pyruvate
reductases is by no means always obvious. For
example, both the sea anemones and the cockle
Cardium edule possess an ODH but do not produce octopine [155]. Opine dehydrogenases are
usually found together with LDH, and a not
insignificant number of species contain more than
one type of opine dehydrogenase; the relative
proportions of the individual pyruvate reductases
vary from tissue to tissue [70]. The species- and
organ-specific spectrum of the pyruvate reductases and the differences in their substrate specificity and kinetic-regulatory properties can probably
be looked upon as adaptations to the speciesspecific spectrum of free amino acids or the different physiological functions of the enzymes. In the
polychaete Aphrodite aculeata, each tissue contains only one opine dehydrogenase: longitudinal
muscles, nervous tissue and scales have a broadspecificity alanopine dehydrogenase and the gut
14.11.3 Opine Dehydrogenases
547
has a highly specific strombine dehydrogenase;
LDH and ODH are both absent [242]. The snail
Busycotypus canaliculatum possesses alan opine
dehydrogenase, ODH and LDH. Alanopine
dehydrogenases are to be found in all the organs
and are important especially during habitatdependent anaerobiosis; ODH occurs mainly in
the muscle, and links phosphagen cleavage and
glycolysis during activity-dependent anaerobiosis; LDH is restricted to the heart ventricle and
the continuously active proboscis muscle [191]. In
the edible mussel Mytilus edulis, the opine dehydrogenase of the gut is alanine specific, whereas
the muscle enzyme, which has a particularly high
glycine concentration, can also efficiently metabolize glycine [190].
Many animals possess different pyruvate
reductases that are active in different physiological situations [84] (Table 14.5). This is of biological advantage when both hypoxic conditions
and the need to escape predators occur in the life
of an animal. The presence of multiple pyruvate
reductases ensures that the products formed in
one reaction do not inhibit the enzymes of the
other reactions [70]. Cardium tubercula tum has
altogether aD-specific LDH, two ODHs, four
alanopine dehydrogenases and a strombine
dehydrogenase. However, activity-dependent
anaerobiosis gives rise exclusively to octopine,
whereas habitat-dependent anaerobiosis produces mainly D-Iactate (in addition to alanine) but
only a little octopine, very little alanopine and no
strombine. This ratio of end products is in accordance with the kinetic-regulatory properties of the
enzymes and the intracellular concentrations of
substrates and co substrates [156].
For the alanopine/strombine dehydrogenase of
Arenicola marina, the ratio of the activities
against alanine and glycine shifts with decreasing
NADH concentration in favour of the latter, so
that during activity-dependent anaerobiosis with
a high rate of glycolysis mainly alanopine is produced, and in habitat-dependent anaerobiosis
with reduced metabolism mainly strombine is
produced, in addition to succinate, propionate
and alanine [231]. Sipunculus nudus produces
mainly octopine during activity-dependent anaerobiosis but strombine during anoxia. However,
the octopine/strombine dualism is not fully
explained by the kinetic properties of ODH and
strombine/alanopine dehydrogenase and by the
concentrations of the substrates and cosubstrates.
There are further cases in which the adjustments
in metabolism are not completely understood:
The activity of the pedal retractor muscle of the