in many invertebrates. They are widely distributed amongst the molluscs and crustaceans which
feed on brown algae or phytoplankton. They are
present in almost all inhabitants of the forest floor
and leaf litter, such as oligochaetes, isopods, chilopods, diplopods and insects. Amongst the laminarinases, a distinction is drawn between the
endo-~(1-3)-glucanases, which cleave internal
bonds, and the exo-~(1-3)-glucanases, which
change the anomeric configuration and release aglucose residues from the non-reducing ends of
~-(1-3)-glucans. The marine copepod Acartia
clausi possesses both types of enzyme with the
exo-activity predominating; this is bound to a
protein of 21 kDa and has a pH optimum of 5.6
[226]. Animals with high laminarinase activity
often have only the endohydrolase but, in contrast to the corresponding enzymes of the fungi
and plants, the animal enzymes are still active
against tri- and disaccharides and therefore can
compensate for the lack of exo-activity [51]. Exo~(1-3)-glucosidases have been detected, for
example, in Helix pomatia, other pulmonate
snails and sea urchin eggs [263]. Several of these
enzymes have been isolated and characterized.
The endohydrolases usually have lower molecular
masses (20-22 kDa) than do the exohydrolases,
which are usually more than 100 kDa. The exceptions to this rule are the endo-~(1-3)-glucanase
isolated from larvae of the beetle Rhagium inquisitor, which is about 100 kDa, and the small exohydrolase from the copepod Acartia, mentioned
above [51, 226, 263]. The crystalline style of the
mussel Chlamys abbidus contains both a ~(1-3)and a ~(1-6)-specific endoglucanase [233].
Further polysaccharide-hydrolysing enzyme
activities are found in the tissues, body fluids and
poisonous secretions of animals, but there are few
comparative biochemical data available. On the
one hand, there are enzymes that attack the cell
wall substances present in herbivore diets, and on
the other hand, there are the enzymes that can
hydrolyse animal proteoglycans. The cell walls of
higher plants consist of cellulose fibres embedded
in a matrix of lignin, hemicelluloses and pectins.
Neither lignin nor the mixture of branched heteroglycans known as hemicellulose are effectively
digested by animal enzymes. The pectins are
made up of a(1-4)-linked galacturonic acid residues which are, in part, methylated. Pectinases
are widely found in fungi and higher plants and
have also been detected in molluscs, coleopterans
and dipterans [102]. Alginases from sea urchins
and marine mussels cleave the alginic acids
found, for example, in the brown algae; these
13.6.4 Chitinolysis
501
consist of ~(1-4)-linked mannuronic acid and
single residues of its 5-epimer L-guluronic acid.
The hyaluronidases and chondroitinases of the
vertebrates are involved in the metabolism of the
extracellular matrix; the hyaluronidases present
at high activity in the venoms of snakes, bees, spiders and scorpions serve in the dissemination of
the toxin in the tissues. The saliva of the leech
Hirudo medicinalis contains an endo-~glucuronidase which is highly specific for hyaluronic acid and which, in contrast to the endo-~hexosaminidases from mammalian connective tissues, does not attack chondroitin. This property
makes the enzyme particularly suitable for cell
separation and it has been marketed under the
name "Orgelase".
13.6.4 Chitinolysis
At least two types of enzyme are required for
the complete hydrolysis of chitin: a chitinase,
which reduces chitin to oligosaccharides, and
a ~-N-acetylglucosaminidase or a -N-acetylhexosaminidase, which releases N-acetylglucosamine.
Chitinases with a digestive function are found in
the entoderm of the Cnidaria and in the gut and
associated glands of many invertebrates. Contrary to early assumptions, these enzymes are
probably not of bacterial origin but are produced
by the animals themselves [100, 151, 172, 192,
248]. The vertebrates show an evolutionary trend
towards loss of chitinases; they are still widely
found in the fish, amphibians and reptiles, but are
absent from most species of birds and mammals
that exist on a herbivorous or otherwise chitinfree diet. Thus, chitinase is present in the gut of
rats, mice, dogs and foxes, but not in the gut of
tortoises, pigeons, rabbits, sheep, cats or humans
[192]. ~-N-Acetylglucosaminidases and N-Nacetylhexosaminidases, which are also required
for the metabolism of proteoglycans and glycoproteins, are probably ubiquitous. It is somewhat
extraordinary to find a high activity of a genuine
chitinase in calf serum. Nematode larvae have a
chitinase of ectodermal origin and this is probably
involved in hatching [192]. The similar ectodermal chitinases that appear at certain times in the
integument of arthropods certainly have a function in moulting. In insects, spiders and crustaceans, during the period between separation of
the cuticula from the epidermis (apolysis) and
moulting itself (ecdysis), up to 90 % of the
material of the old cuticula is released, reabsorbed and reused [50, 247].
feed on brown algae or phytoplankton. They are
present in almost all inhabitants of the forest floor
and leaf litter, such as oligochaetes, isopods, chilopods, diplopods and insects. Amongst the laminarinases, a distinction is drawn between the
endo-~(1-3)-glucanases, which cleave internal
bonds, and the exo-~(1-3)-glucanases, which
change the anomeric configuration and release aglucose residues from the non-reducing ends of
~-(1-3)-glucans. The marine copepod Acartia
clausi possesses both types of enzyme with the
exo-activity predominating; this is bound to a
protein of 21 kDa and has a pH optimum of 5.6
[226]. Animals with high laminarinase activity
often have only the endohydrolase but, in contrast to the corresponding enzymes of the fungi
and plants, the animal enzymes are still active
against tri- and disaccharides and therefore can
compensate for the lack of exo-activity [51]. Exo~(1-3)-glucosidases have been detected, for
example, in Helix pomatia, other pulmonate
snails and sea urchin eggs [263]. Several of these
enzymes have been isolated and characterized.
The endohydrolases usually have lower molecular
masses (20-22 kDa) than do the exohydrolases,
which are usually more than 100 kDa. The exceptions to this rule are the endo-~(1-3)-glucanase
isolated from larvae of the beetle Rhagium inquisitor, which is about 100 kDa, and the small exohydrolase from the copepod Acartia, mentioned
above [51, 226, 263]. The crystalline style of the
mussel Chlamys abbidus contains both a ~(1-3)and a ~(1-6)-specific endoglucanase [233].
Further polysaccharide-hydrolysing enzyme
activities are found in the tissues, body fluids and
poisonous secretions of animals, but there are few
comparative biochemical data available. On the
one hand, there are enzymes that attack the cell
wall substances present in herbivore diets, and on
the other hand, there are the enzymes that can
hydrolyse animal proteoglycans. The cell walls of
higher plants consist of cellulose fibres embedded
in a matrix of lignin, hemicelluloses and pectins.
Neither lignin nor the mixture of branched heteroglycans known as hemicellulose are effectively
digested by animal enzymes. The pectins are
made up of a(1-4)-linked galacturonic acid residues which are, in part, methylated. Pectinases
are widely found in fungi and higher plants and
have also been detected in molluscs, coleopterans
and dipterans [102]. Alginases from sea urchins
and marine mussels cleave the alginic acids
found, for example, in the brown algae; these
13.6.4 Chitinolysis
501
consist of ~(1-4)-linked mannuronic acid and
single residues of its 5-epimer L-guluronic acid.
The hyaluronidases and chondroitinases of the
vertebrates are involved in the metabolism of the
extracellular matrix; the hyaluronidases present
at high activity in the venoms of snakes, bees, spiders and scorpions serve in the dissemination of
the toxin in the tissues. The saliva of the leech
Hirudo medicinalis contains an endo-~glucuronidase which is highly specific for hyaluronic acid and which, in contrast to the endo-~hexosaminidases from mammalian connective tissues, does not attack chondroitin. This property
makes the enzyme particularly suitable for cell
separation and it has been marketed under the
name "Orgelase".
13.6.4 Chitinolysis
At least two types of enzyme are required for
the complete hydrolysis of chitin: a chitinase,
which reduces chitin to oligosaccharides, and
a ~-N-acetylglucosaminidase or a -N-acetylhexosaminidase, which releases N-acetylglucosamine.
Chitinases with a digestive function are found in
the entoderm of the Cnidaria and in the gut and
associated glands of many invertebrates. Contrary to early assumptions, these enzymes are
probably not of bacterial origin but are produced
by the animals themselves [100, 151, 172, 192,
248]. The vertebrates show an evolutionary trend
towards loss of chitinases; they are still widely
found in the fish, amphibians and reptiles, but are
absent from most species of birds and mammals
that exist on a herbivorous or otherwise chitinfree diet. Thus, chitinase is present in the gut of
rats, mice, dogs and foxes, but not in the gut of
tortoises, pigeons, rabbits, sheep, cats or humans
[192]. ~-N-Acetylglucosaminidases and N-Nacetylhexosaminidases, which are also required
for the metabolism of proteoglycans and glycoproteins, are probably ubiquitous. It is somewhat
extraordinary to find a high activity of a genuine
chitinase in calf serum. Nematode larvae have a
chitinase of ectodermal origin and this is probably
involved in hatching [192]. The similar ectodermal chitinases that appear at certain times in the
integument of arthropods certainly have a function in moulting. In insects, spiders and crustaceans, during the period between separation of
the cuticula from the epidermis (apolysis) and
moulting itself (ecdysis), up to 90 % of the
material of the old cuticula is released, reabsorbed and reused [50, 247].