pean dogs but NeuGc in Oriental dogs; exclusively NeuGc in the horse, giant panda and
domestic cat; and both NeuAc and NeuGc in Persian cats [281].
The gangliosides of the brain show the highest
concentrations and complexity; in the synaptosome membranes they constitute up to 15 % of the
total lipids. Critical to their function is the fact
that they are the only lipids to change in properties after binding calcium ions, and they are therefore probably modulators of synaptic signal transmission. Intensive comparative investigations of
representatives of all the vertebrates groups from
the elasmobranchs to the mammals have shown
the following [7, 95, 213, 214, 215]:
1. The brain gangliosides of the vertebrates
belong almost exclusively to the ganglioseries, whereby lactose and gangliotriaose predominate in the elasmobranchs, and gangliotetraose predominates in all other vertebrates
up to the mammals.
2. Despite large species-specific differences, the
ganglioside concentrations in the brain clearly
increase in the vertebrate order, with values of
0.5-1.0 nmol ganglioside-bound sialic acid per
g fresh weight in the fish and amphibians, more
than 1.3-1.7 nmol/g in the reptiles, and up to
2-3 nmol/g in the birds and mammals. It is
noteworthy that all elasmobranchs have relatively high values, and highly developed forms,
such as Myliobatis australis, show higher values
(1.88 nmol/g) than do primitive species such as
Squalus acanthias (0.87 nmol/g).
3. The spectrum of brain gangliosides differs
between the different sections of the brain.
However, there is a clear trend towards simplicity with increasing brain organization. In the
lower poikilothermic vertebrates there is a
large number of complex gangliosides that
have many sialic groups; in contrast, in the
birds and mammals there is a lower number of
less strongly polar gangliosides. Similarly, in
the mammals the ganglioside spectrum decreases in complexity from the monotremes to the
marsupials to the Placentalia [213, 214]. Simplification of the spectrum with increasing
degree of organization is also observed for
other metabolites, e.g. the sterols. The phenomenon can be explained by the assumption
that nature began with experiments involving
several different substances, and with time
selected those that were most suitable. The
agnathan Lampetra fluviatilis has one-third
each of di-, tri- and tetrasialogangliosides,
15.4.4 Glycolipids
609
80 % of which are produced by the b pathway
(Fig. 15.27). In the elasmobranchs, pentasialoand hexasialo- compounds constitute 18-25 %
of the gangliosides. The brain gangliosides of
the many teleosts to have been investigated
differ greatly in polarity. This is probably
related to the average temperature of their
habitats. Strongly polar gangliosides at low
temperatures have the same calcium-binding
capacity as do less polar forms at higher temperatures. Thus, the tropical tapir fish Gnathonemus petersi has 16 % monosialoganglioside
and 45 % disialoganglioside, whereas the
Antarctic ice fish Trematomus hansoni has the
most polar ganglioside spectrum of all vertebrates with 40 % pentasialo- and hexasialocompounds. In the mammals, on the other
hand, 68-84 % of the gangliosides have only
one or two sialic acids, 8-22 % have three
sialic acids, and only 4-12 % have four or
more sialic acids. The proportion of gangliosides with a high number of sialic acids increases
during hibernation. The relationship between
calcium binding, polarity and temperature
explains why changes in the spectrum of brain
gangliosides is among the mechanisms of
adaptation to temperature found in the vertebrates [213, 214).
4. Alteration of the ganglioside spectrum is
accompanied by a change in the synthetic
pathway (Fig. 15.27). The b pathway predominates in the agnathans; the Chondrichthyes
and Osteichthyeses have in addition the c
pathway, which is clearly the dominant pathway in the higher teleosts, such as the pike
Esox lucius. Both the band c pathways are
also found in the amphibians, whereas reptiles
and birds use the a and b pathways. Finally, the
mammals have only the a pathway [213,214].
During ontogenesis in the chicken, there is a
"recapitulation of the phylogeny" in that the
embryo makes use of the more primitive combination of the band c pathways, whereas the
adult utilizes a and b.
Glycoglycerolipids have been found only so far in
vertebrate sperm and myelin. The main representative of this class in mammalian sperm is the
l-alkyl-2-acyl compound known as seminolipid
(Fig. 15 .25b). This is also found in the rat brain,
together with the corresponding diacyl compound; in contrast, the brain of the cod Gadus
morrhua contains only the diacylated form [281].
Glycoglycerolipids with a rather peculiar structure have been isolated from the cockroach
domestic cat; and both NeuAc and NeuGc in Persian cats [281].
The gangliosides of the brain show the highest
concentrations and complexity; in the synaptosome membranes they constitute up to 15 % of the
total lipids. Critical to their function is the fact
that they are the only lipids to change in properties after binding calcium ions, and they are therefore probably modulators of synaptic signal transmission. Intensive comparative investigations of
representatives of all the vertebrates groups from
the elasmobranchs to the mammals have shown
the following [7, 95, 213, 214, 215]:
1. The brain gangliosides of the vertebrates
belong almost exclusively to the ganglioseries, whereby lactose and gangliotriaose predominate in the elasmobranchs, and gangliotetraose predominates in all other vertebrates
up to the mammals.
2. Despite large species-specific differences, the
ganglioside concentrations in the brain clearly
increase in the vertebrate order, with values of
0.5-1.0 nmol ganglioside-bound sialic acid per
g fresh weight in the fish and amphibians, more
than 1.3-1.7 nmol/g in the reptiles, and up to
2-3 nmol/g in the birds and mammals. It is
noteworthy that all elasmobranchs have relatively high values, and highly developed forms,
such as Myliobatis australis, show higher values
(1.88 nmol/g) than do primitive species such as
Squalus acanthias (0.87 nmol/g).
3. The spectrum of brain gangliosides differs
between the different sections of the brain.
However, there is a clear trend towards simplicity with increasing brain organization. In the
lower poikilothermic vertebrates there is a
large number of complex gangliosides that
have many sialic groups; in contrast, in the
birds and mammals there is a lower number of
less strongly polar gangliosides. Similarly, in
the mammals the ganglioside spectrum decreases in complexity from the monotremes to the
marsupials to the Placentalia [213, 214]. Simplification of the spectrum with increasing
degree of organization is also observed for
other metabolites, e.g. the sterols. The phenomenon can be explained by the assumption
that nature began with experiments involving
several different substances, and with time
selected those that were most suitable. The
agnathan Lampetra fluviatilis has one-third
each of di-, tri- and tetrasialogangliosides,
15.4.4 Glycolipids
609
80 % of which are produced by the b pathway
(Fig. 15.27). In the elasmobranchs, pentasialoand hexasialo- compounds constitute 18-25 %
of the gangliosides. The brain gangliosides of
the many teleosts to have been investigated
differ greatly in polarity. This is probably
related to the average temperature of their
habitats. Strongly polar gangliosides at low
temperatures have the same calcium-binding
capacity as do less polar forms at higher temperatures. Thus, the tropical tapir fish Gnathonemus petersi has 16 % monosialoganglioside
and 45 % disialoganglioside, whereas the
Antarctic ice fish Trematomus hansoni has the
most polar ganglioside spectrum of all vertebrates with 40 % pentasialo- and hexasialocompounds. In the mammals, on the other
hand, 68-84 % of the gangliosides have only
one or two sialic acids, 8-22 % have three
sialic acids, and only 4-12 % have four or
more sialic acids. The proportion of gangliosides with a high number of sialic acids increases
during hibernation. The relationship between
calcium binding, polarity and temperature
explains why changes in the spectrum of brain
gangliosides is among the mechanisms of
adaptation to temperature found in the vertebrates [213, 214).
4. Alteration of the ganglioside spectrum is
accompanied by a change in the synthetic
pathway (Fig. 15.27). The b pathway predominates in the agnathans; the Chondrichthyes
and Osteichthyeses have in addition the c
pathway, which is clearly the dominant pathway in the higher teleosts, such as the pike
Esox lucius. Both the band c pathways are
also found in the amphibians, whereas reptiles
and birds use the a and b pathways. Finally, the
mammals have only the a pathway [213,214].
During ontogenesis in the chicken, there is a
"recapitulation of the phylogeny" in that the
embryo makes use of the more primitive combination of the band c pathways, whereas the
adult utilizes a and b.
Glycoglycerolipids have been found only so far in
vertebrate sperm and myelin. The main representative of this class in mammalian sperm is the
l-alkyl-2-acyl compound known as seminolipid
(Fig. 15 .25b). This is also found in the rat brain,
together with the corresponding diacyl compound; in contrast, the brain of the cod Gadus
morrhua contains only the diacylated form [281].
Glycoglycerolipids with a rather peculiar structure have been isolated from the cockroach