532
14 Glycolysis
aerobic functioning muscles show little or no
regulation. PKs similar to PK-M1 of the mammals
are found, for example, in the skeletal muscles of
crabs, the flight muscles of insects and the mantle
muscles of the cephalopods [36, 53,63, 173,245].
However, the PK from the muscles of the crayfish
Oreoneetes limosus exists in two forms with different substrate affinities, the high-affinity form
being stabilized by Fru-l,6-P2• The whole range of
PKs is found in the molluscs, from the hardly
regulated PK of cephalopod muscles, which
resemble most closely mammalian PK-Mb
through the Mz-like PKs to those which have
levels of allosteric modulation and covalent modification just as complex as those of mammalian
liver PK-L [36]. Allosterically regulated muscle
PKs have been investigated in detail in, for example, the mussels Crassostrea, Cardium, Mytilus,
Seapharea and ~nus, and the South American
purple snail Coneholepas [29, 36,40, 99].
The aUosteric effectors of the invertebrate PKs
are, in particular, Fru-l,6-P2, ATP and alanine or
other amino acids [173]. The frequently observed
inhibitory effects of phosphagens is probably an
artefact produced by crude extracts in which the
phosphagen kinase that is always present uses up
the PK substrate, ADP. A reduction in pH brings
about the inhibition of PK and the stimulation of
PEPCK in marine mussels, and thus a switch
from pyruvate production to the more efficient
succinate pathway of anaerobic energy production. The pH effect is much less marked in the
freshwater mussel Anodonta eygnea [105,224].
Bicarbonate inhibits PK and activates PEPCK,
for example, in the oligochaete Tubi[ex and the
cestode Hymenolepis diminuta. There have been
reports of alanine inhibition of PK from cnidarians, bivalves and crustaceans but not from Tubi[ex or the frog.
The regulation of PK by allosteric effectors and
pH is complemented in many molluscs by covalent modification. In particular, in anoxia-tolerant
species, such as Mytilus edulis, Patella eaerulea
and Busyeotypus (Busyeon) eanalieulatum, but
also in the drought-resistant terrestrial snail Otala
laetea the muscle PK is subject to phosphorylation [157, 158, 275]. A PK-specific protein kinase
has been isolated from B. eanalieulatum [19]. The
substrate constant for PEP is increased by phosphorylation, and the inhibitor constant for ATP
and L-alanine is reduced; the end result is thus a
reduction in PK activity. However, the converse
has been observed for the PK from adductor
muscles of the bivalves ~nus gallina and Seapharea inaequivalis; in this case, PEP affinity and
enzyme activity are increased after in vitro phosphorylation by added cAMP-dependent protein
kinase [88].
Some pyruvate kinases of the Protozoa have
rather unusual properties. For example, the PK
from Leishmania donovani shows sigmoidal PEP
kinetics, and thus homotropic interaction, but it
exhibits no allosteric effects. In contrast, Fru-l,6P2 and in particular Fru-2,6-P2 reduce cooperativity and increase the affinity of PK from Trypanosoma eruzi and T. brueei; ATP counteracts this
effect [25, 222]. Entamoeba histoloytiea possesses
a diphosphotransferase instead of a typical PK, a
situation otherwise found only in plants. In contrast to PK, this enzyme catalyses a reversible
reaction:
PEP + AMP + PPj ~ = pyruvate + ATP + Pj.
(14.1)
14.8 Further Glycolysis Enzymes
Compared with the six enzymes discussed above,
the remaining enzymes of the glycolysis pathway
have received much less attention from comparative biochemistry. Phosphoglucomutase has been
isolated from mammals, teleosts and elasmobranchs, as well as from higher plants and lower
fungi. All examples have a molecular mass of
62-63 kDa, and the great similarity between the
amino acid compositions of the enzymes from
various fish, the rabbit and the potato is indicative of a relatively slow evolution. The sequence is
known only for the rabbit enzyme [200]. Glucose
phosphate isomerase (GPI) from the trypanosomes to the mammals has very similar properties.
Whereas the tetrapod vertebrates (amphibians to
mammals) have only one GPI locus, the teleosts
(except for the Clupeomorpha) have two isoenzymes that differ in their tissue location and catalytic properties; GPI-A predominates in muscle,
and GPI-B predominates in the liver and other
organs [13]. Two GPI loci are also found in the
agnathans of the order Petromyzontoidea, but
only one locus is found in the order Myxinoidea,
the cartilaginous fish and the ancient actinoptergygians of the genera Amia and Lepisosteus.
Branehiostoma and the ascidian Ciona also have
only one GPI. The explanation for this distribution probably lies in independent duplications of
the GPI gene in the development of the lampreys
and the teleosts, and loss of one of the genes in
the Clupeomorpha [38, 97].
14 Glycolysis
aerobic functioning muscles show little or no
regulation. PKs similar to PK-M1 of the mammals
are found, for example, in the skeletal muscles of
crabs, the flight muscles of insects and the mantle
muscles of the cephalopods [36, 53,63, 173,245].
However, the PK from the muscles of the crayfish
Oreoneetes limosus exists in two forms with different substrate affinities, the high-affinity form
being stabilized by Fru-l,6-P2• The whole range of
PKs is found in the molluscs, from the hardly
regulated PK of cephalopod muscles, which
resemble most closely mammalian PK-Mb
through the Mz-like PKs to those which have
levels of allosteric modulation and covalent modification just as complex as those of mammalian
liver PK-L [36]. Allosterically regulated muscle
PKs have been investigated in detail in, for example, the mussels Crassostrea, Cardium, Mytilus,
Seapharea and ~nus, and the South American
purple snail Coneholepas [29, 36,40, 99].
The aUosteric effectors of the invertebrate PKs
are, in particular, Fru-l,6-P2, ATP and alanine or
other amino acids [173]. The frequently observed
inhibitory effects of phosphagens is probably an
artefact produced by crude extracts in which the
phosphagen kinase that is always present uses up
the PK substrate, ADP. A reduction in pH brings
about the inhibition of PK and the stimulation of
PEPCK in marine mussels, and thus a switch
from pyruvate production to the more efficient
succinate pathway of anaerobic energy production. The pH effect is much less marked in the
freshwater mussel Anodonta eygnea [105,224].
Bicarbonate inhibits PK and activates PEPCK,
for example, in the oligochaete Tubi[ex and the
cestode Hymenolepis diminuta. There have been
reports of alanine inhibition of PK from cnidarians, bivalves and crustaceans but not from Tubi[ex or the frog.
The regulation of PK by allosteric effectors and
pH is complemented in many molluscs by covalent modification. In particular, in anoxia-tolerant
species, such as Mytilus edulis, Patella eaerulea
and Busyeotypus (Busyeon) eanalieulatum, but
also in the drought-resistant terrestrial snail Otala
laetea the muscle PK is subject to phosphorylation [157, 158, 275]. A PK-specific protein kinase
has been isolated from B. eanalieulatum [19]. The
substrate constant for PEP is increased by phosphorylation, and the inhibitor constant for ATP
and L-alanine is reduced; the end result is thus a
reduction in PK activity. However, the converse
has been observed for the PK from adductor
muscles of the bivalves ~nus gallina and Seapharea inaequivalis; in this case, PEP affinity and
enzyme activity are increased after in vitro phosphorylation by added cAMP-dependent protein
kinase [88].
Some pyruvate kinases of the Protozoa have
rather unusual properties. For example, the PK
from Leishmania donovani shows sigmoidal PEP
kinetics, and thus homotropic interaction, but it
exhibits no allosteric effects. In contrast, Fru-l,6P2 and in particular Fru-2,6-P2 reduce cooperativity and increase the affinity of PK from Trypanosoma eruzi and T. brueei; ATP counteracts this
effect [25, 222]. Entamoeba histoloytiea possesses
a diphosphotransferase instead of a typical PK, a
situation otherwise found only in plants. In contrast to PK, this enzyme catalyses a reversible
reaction:
PEP + AMP + PPj ~ = pyruvate + ATP + Pj.
(14.1)
14.8 Further Glycolysis Enzymes
Compared with the six enzymes discussed above,
the remaining enzymes of the glycolysis pathway
have received much less attention from comparative biochemistry. Phosphoglucomutase has been
isolated from mammals, teleosts and elasmobranchs, as well as from higher plants and lower
fungi. All examples have a molecular mass of
62-63 kDa, and the great similarity between the
amino acid compositions of the enzymes from
various fish, the rabbit and the potato is indicative of a relatively slow evolution. The sequence is
known only for the rabbit enzyme [200]. Glucose
phosphate isomerase (GPI) from the trypanosomes to the mammals has very similar properties.
Whereas the tetrapod vertebrates (amphibians to
mammals) have only one GPI locus, the teleosts
(except for the Clupeomorpha) have two isoenzymes that differ in their tissue location and catalytic properties; GPI-A predominates in muscle,
and GPI-B predominates in the liver and other
organs [13]. Two GPI loci are also found in the
agnathans of the order Petromyzontoidea, but
only one locus is found in the order Myxinoidea,
the cartilaginous fish and the ancient actinoptergygians of the genera Amia and Lepisosteus.
Branehiostoma and the ascidian Ciona also have
only one GPI. The explanation for this distribution probably lies in independent duplications of
the GPI gene in the development of the lampreys
and the teleosts, and loss of one of the genes in
the Clupeomorpha [38, 97].