7. MONOSACCHARIDES AND OLIGOSACCHARIDES
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latter occurs in the marine algae Irideae laminaroides (93), Gelidium
pristoides (94), and Gracilaria confervoides (94); it has recently been
found in wheat flour (95). The oligosaccharides of milk (Section VI,B)
contain D-galactose.
Polysaccharides (96) composed wholly or partly of D-galactose units
are numerous. These include hemicelluloses, plant gums, and mucilages
(97), algal polysaccharides (98), and some elaborated by bacteria and
molds (96), a galactan of mammalian (beef) lung (99), frog spawn
(100), and the galactan (galactogen) elaborated by the "albumin
gland" of the vineyard snail (Helix pomatia), in which it is accompanied by L-galactose in the proportion of 1-6 moles (101). It is not
known whether the L-sugar occurs in the "albumin gland" secretion of
other species of Helix, but four species of aquatic snails have been
examined and found to possess galactose-containing polysaccharides in
which fucose and other sugars are present (101a).
The constituents of vertebrate nervous tissue, the gangliosides and
cerebrosides (75) already mentioned, contain D-galactose. Most glycoproteins (102), that is, proteins containing a carbohydrate-derived
moiety, almost invariably contain some galactose; very few proteins, as
we know them, are completely devoid of carbohydrate. Indeed, the
well-known Mölisch reaction for carbohydrates was originally devised
as a test for proteins. Galactose is found in blood plasma proteins,
mucous secretions, egg proteins (103), and the blood-group substances
(104); in all these, other sugars occur as well, glucose among the common monosaccharides being absent. Microorganisms of many types
elaborate macromolecules in which D-galactose (105)* is a major or a
minor component.
3. Combined v-Galactofuranose
Penicillium charlesii G. Smith produces in its culture media a galactan which is unique in that it is composed of D-galactofuranose units
(106). The D-arabitol-O-D-galactoside, umbilicin, isolated from lichens
of the Order Gymnocarpeae, e.g., Umbilicaria pustulata, likewise has its
sugar moiety in the furanose form (106a). Certain of the units of the
polysaccharide of Cladophora rupestris are derived from D-galactofuranose (106b).
E. L-GALACTOSE
The sugar is unknown in the uncombined condition. Besides being
present in Helix pomatia galactogen (see above) and in the jelly coat
* Penicillium varians makes a heteropolysaccharide in which the unit chains contain D-glucose at the nonreducing end; the reducing end is terminated by D-idose
or D-altrose (105).
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latter occurs in the marine algae Irideae laminaroides (93), Gelidium
pristoides (94), and Gracilaria confervoides (94); it has recently been
found in wheat flour (95). The oligosaccharides of milk (Section VI,B)
contain D-galactose.
Polysaccharides (96) composed wholly or partly of D-galactose units
are numerous. These include hemicelluloses, plant gums, and mucilages
(97), algal polysaccharides (98), and some elaborated by bacteria and
molds (96), a galactan of mammalian (beef) lung (99), frog spawn
(100), and the galactan (galactogen) elaborated by the "albumin
gland" of the vineyard snail (Helix pomatia), in which it is accompanied by L-galactose in the proportion of 1-6 moles (101). It is not
known whether the L-sugar occurs in the "albumin gland" secretion of
other species of Helix, but four species of aquatic snails have been
examined and found to possess galactose-containing polysaccharides in
which fucose and other sugars are present (101a).
The constituents of vertebrate nervous tissue, the gangliosides and
cerebrosides (75) already mentioned, contain D-galactose. Most glycoproteins (102), that is, proteins containing a carbohydrate-derived
moiety, almost invariably contain some galactose; very few proteins, as
we know them, are completely devoid of carbohydrate. Indeed, the
well-known Mölisch reaction for carbohydrates was originally devised
as a test for proteins. Galactose is found in blood plasma proteins,
mucous secretions, egg proteins (103), and the blood-group substances
(104); in all these, other sugars occur as well, glucose among the common monosaccharides being absent. Microorganisms of many types
elaborate macromolecules in which D-galactose (105)* is a major or a
minor component.
3. Combined v-Galactofuranose
Penicillium charlesii G. Smith produces in its culture media a galactan which is unique in that it is composed of D-galactofuranose units
(106). The D-arabitol-O-D-galactoside, umbilicin, isolated from lichens
of the Order Gymnocarpeae, e.g., Umbilicaria pustulata, likewise has its
sugar moiety in the furanose form (106a). Certain of the units of the
polysaccharide of Cladophora rupestris are derived from D-galactofuranose (106b).
E. L-GALACTOSE
The sugar is unknown in the uncombined condition. Besides being
present in Helix pomatia galactogen (see above) and in the jelly coat
* Penicillium varians makes a heteropolysaccharide in which the unit chains contain D-glucose at the nonreducing end; the reducing end is terminated by D-idose
or D-altrose (105).