14.10.1 Activity- and Habitat-Dependent Anaerobiosis
535
iments have demonstrated the formation of glucose from lactate in the muscles of fish, amphibians and mammals. Here, the PC reaction is
replaced by a combination of malic enzyme and
malate dehydrogenase (Fig. 14.1). Muscle gluconeogenesis in the vertebrates is restricted to certain types of fibre, and in fish, amphibians and
reptiles it is probably only significant in the red
muscles [78, 170]. PC has been detected in the
muscles of some teleosts, the only case known in
the vertebrates, and otherwise is found at high
activities only in insect flight muscles [170].
Lactate also reaches high levels in the haemolymph of malacostracan crustaceaus during brisk
muscle activity but, in contrast to the situation in
the mammals, it is removed only very slowly from
the blood. For example, in the lobster Homarus
gammarus and in the crayfish Cherax destructor it
requires about 6 h, compared with 30 min in
humans. The hepatopancreas, which as a central
organ for metabolism is often compared with the
liver, has no capacity for gluconeogenesis from
lactate.
14.10 Anaerobiosis
14.10.1 Activity- and Habitat-Dependent
Anaerobiosis
In the presence of an adequate supply of oxygen,
carbohydrates are completely catabolized to CO2
and H20 with the production of energy, the theoretical yield being 38 ATPs per glucose residue of
glycogen. However, in their natural habitats
many animals experience a transient or long-term
deficiency of oxygen (hypoxia), or the complete
absence of oxygen (anoxia), and must therefore
be capable of anaerobic energy production
(habitat-dependent anaerobiosis). An anaerobic
energy-yielding process is also necessary when
the energy requirement of the muscles during active locomotory effort exceeds the capacity of the
aerobic process (activity-dependent anaerobiosis). The various anaerobic mechanisms for
obtaining energy in the animal kingdom are interesting examples of biochemical adaptation. They
have, therefore, been widely investigated and
extensively reviewed [21, 83, 102].
Activity-dependent anaerobiosis occurs only as
a consequence of sudden, transient enhanced
muscle activity, e.g. in fleeing from predators or
catching prey. In contrast, muscles that operate
continuously at high activity, e.g. the flight muscles of insects or birds, are dependent upon
aerobic energy production. Activity-dependent
anaerobiosis is widely found in the animal kingdom. A typical example is the white muscle of
vertebrates, especially of amphibians and fish,
and also of some invertebrates. The cephalopods
achieve high swim-velocities by the rapid ejection
of water from the mantle cavity by the contraction
of mantle muscles; however, the musculature is
usually exhausted after 10-20 such contractions.
The scallops (Pectinoidea) can escape attack from
starfish by swimming; they clap their shells together by contracting the shell-closing muscles
(adductors), thereby propelling themselves. In
this case, the muscles are also exhausted after
30-50 contractions. The cockle Cardium tuberculatum executes jumping movements to escape
starfish. The closely related species C. edule, like
other mussels, only uses the foot musculature to
bury itself. This occurs particularly rapidly in the
case of the razor shell Ensis directus. The common whelk Buccinum undatum escapes from predators by executing rotating movements brought
about by the columellar muscle. The worms
Sipunculus nudus and Arenicola marina bury
themselves rapidly in the mud; in experiments,
they perform this action several times until the
muscles of the body wall become exhausted. In
the characteristic defence reaction of the crayfish,
the posterior body section is thrust forward by
contraction of the abdominal muscles, and the
animal springs backwards. Several types of insect
muscle, e.g. the jumping muscles of the locust,
also show activity-dependent anaerobiosis. In
most vertebrates, anaerobic metabolism in muscles is only necessary at the commencement of
locomotory activity, and continues until the oxygen supply to the muscle is adequately reinforced.
However, in many terrestrial and all aquatic
amphibian species the energy requirements for
locomotion are always predominantly derived
from anaerobic processes [161, 198].
At the onset of sudden muscle activity, the rate
of ATP cleavage increases manyfold without a
concomitant increase in the oxygen supply.
RephosphoryJation of ADP at first makes use of
the energy-rich phosphate stored in phosphagen.
Only when this is exhausted does the muscle
revert to degradation of glycogen to cover its
energy requirements. This occurs anaerobically
only to the extent to which the aerobic process is
insufficient. For example, in the swimming scallop Placopecten magellanicus glycogen catabolism is about 3 % aerobic, but because of its far
greater effectiveness this covers about one-third
535
iments have demonstrated the formation of glucose from lactate in the muscles of fish, amphibians and mammals. Here, the PC reaction is
replaced by a combination of malic enzyme and
malate dehydrogenase (Fig. 14.1). Muscle gluconeogenesis in the vertebrates is restricted to certain types of fibre, and in fish, amphibians and
reptiles it is probably only significant in the red
muscles [78, 170]. PC has been detected in the
muscles of some teleosts, the only case known in
the vertebrates, and otherwise is found at high
activities only in insect flight muscles [170].
Lactate also reaches high levels in the haemolymph of malacostracan crustaceaus during brisk
muscle activity but, in contrast to the situation in
the mammals, it is removed only very slowly from
the blood. For example, in the lobster Homarus
gammarus and in the crayfish Cherax destructor it
requires about 6 h, compared with 30 min in
humans. The hepatopancreas, which as a central
organ for metabolism is often compared with the
liver, has no capacity for gluconeogenesis from
lactate.
14.10 Anaerobiosis
14.10.1 Activity- and Habitat-Dependent
Anaerobiosis
In the presence of an adequate supply of oxygen,
carbohydrates are completely catabolized to CO2
and H20 with the production of energy, the theoretical yield being 38 ATPs per glucose residue of
glycogen. However, in their natural habitats
many animals experience a transient or long-term
deficiency of oxygen (hypoxia), or the complete
absence of oxygen (anoxia), and must therefore
be capable of anaerobic energy production
(habitat-dependent anaerobiosis). An anaerobic
energy-yielding process is also necessary when
the energy requirement of the muscles during active locomotory effort exceeds the capacity of the
aerobic process (activity-dependent anaerobiosis). The various anaerobic mechanisms for
obtaining energy in the animal kingdom are interesting examples of biochemical adaptation. They
have, therefore, been widely investigated and
extensively reviewed [21, 83, 102].
Activity-dependent anaerobiosis occurs only as
a consequence of sudden, transient enhanced
muscle activity, e.g. in fleeing from predators or
catching prey. In contrast, muscles that operate
continuously at high activity, e.g. the flight muscles of insects or birds, are dependent upon
aerobic energy production. Activity-dependent
anaerobiosis is widely found in the animal kingdom. A typical example is the white muscle of
vertebrates, especially of amphibians and fish,
and also of some invertebrates. The cephalopods
achieve high swim-velocities by the rapid ejection
of water from the mantle cavity by the contraction
of mantle muscles; however, the musculature is
usually exhausted after 10-20 such contractions.
The scallops (Pectinoidea) can escape attack from
starfish by swimming; they clap their shells together by contracting the shell-closing muscles
(adductors), thereby propelling themselves. In
this case, the muscles are also exhausted after
30-50 contractions. The cockle Cardium tuberculatum executes jumping movements to escape
starfish. The closely related species C. edule, like
other mussels, only uses the foot musculature to
bury itself. This occurs particularly rapidly in the
case of the razor shell Ensis directus. The common whelk Buccinum undatum escapes from predators by executing rotating movements brought
about by the columellar muscle. The worms
Sipunculus nudus and Arenicola marina bury
themselves rapidly in the mud; in experiments,
they perform this action several times until the
muscles of the body wall become exhausted. In
the characteristic defence reaction of the crayfish,
the posterior body section is thrust forward by
contraction of the abdominal muscles, and the
animal springs backwards. Several types of insect
muscle, e.g. the jumping muscles of the locust,
also show activity-dependent anaerobiosis. In
most vertebrates, anaerobic metabolism in muscles is only necessary at the commencement of
locomotory activity, and continues until the oxygen supply to the muscle is adequately reinforced.
However, in many terrestrial and all aquatic
amphibian species the energy requirements for
locomotion are always predominantly derived
from anaerobic processes [161, 198].
At the onset of sudden muscle activity, the rate
of ATP cleavage increases manyfold without a
concomitant increase in the oxygen supply.
RephosphoryJation of ADP at first makes use of
the energy-rich phosphate stored in phosphagen.
Only when this is exhausted does the muscle
revert to degradation of glycogen to cover its
energy requirements. This occurs anaerobically
only to the extent to which the aerobic process is
insufficient. For example, in the swimming scallop Placopecten magellanicus glycogen catabolism is about 3 % aerobic, but because of its far
greater effectiveness this covers about one-third