General Properties, Occurrence, and Preparation
1.2
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transucrase from L. mesenteroides NRRL B-512F. It has 95% α-(1→6) linkages with 5%
α-(1→3) branch linkages that have branches that are both single glucose residues and long α(1→6) linked chains and contains ∼10 6 to 10 8 D-glucopyranose residues. Other strains make
a wide variety of dextrans with various degrees of branching, not only through α-(1→3) linkages, but through α-(1→2) and/or α-(1→4) linkages as well. In some cases, the degree of
branching is as low as 3%, and in other instances, virtually every glucose residue in the backbone may be substituted with a branch linkage [41].
Some of these bacteria also elaborate glucansucrases that synthesize polysaccharides that are
not considered dextrans because they do not have contiguous α-(1→6) linked main chains.
L. mesenteroides NRRL B-1355 secretes a dextransucrase that synthesizes a B-512F-type dextran and another enzyme, alternansucrase, that synthesizes an α-glucan from sucrose that has
alternating α-(1→6) and α-(1→3) linked glucose residues in the main chains with 7–11%
α-(1→3) branch chains of alternating α-(1→6) and α-(1→3) linked glucose residues [41].
This α-glucan is called alternan. Another glucansucrase, mutansucrase, secreted by Streptococcus mutans, synthesizes a linear glucan in which the D-glucopyranose residues are linked
α-(1→3). It is particularly characterized by being extremely water-insoluble in contrast to the
dextrans and alternan that are highly water-soluble [41].
Pullulan is a polysaccharide that is elaborated by several species of the fungus, Aureobasidium, particularly A. pullulans. This fungus is typified by the presence of black pigments and
is sometimes called “black yeast” [43]. Pullulan is a water-soluble, linear polysaccharide of
D-glucopyranose residues joined together by a repeating sequence of two α-(1→4) and one
α-(1→6) linkages. The structure is that of a polymer of maltotriose units joined together end
to end by α-(1→6) linkages [44,45,46]. In addition to maltotriose units, it also has ∼5–7%
maltotetraose units located in the interior of the polysaccharide chain [47].
These bacterial polysaccharides have been considered to be “slimes”; they are often in reality
loose capsules that are produced extracellularly by the bacteria. It was found that low molecular weight L. mesenteroides NRRL B-512F dextran could be used as a blood plasma extender
and was produced on a relatively large scale during the “cold war”, but also found uses as
a gel-filtration material when cross-linked by epichlorohydrin to give a family of cross-linked
dextrans [41].
5.4 Properties and Occurrence of D-Glucose in Cyclic Dextrins
A number of different kinds of nonreducing cyclic dextrins containing D-glucopyranose
residues occur. The first to be observed were the cyclomaltodextrins (sometimes referred to
in the older literature as cyclodextrins or Schardinger dextrins), which have been known for
over 100 years. They were first found in rotting vegetables and then in the fermentation of
starch by a heat-resistant microorganism called Bacillus macerans. The compounds were
crystallized from alcohol solutions and shown to be α-(1→4) linked, nonreducing, cyclic dextrins composed of six, seven, and eight D-glucopyranose residues, named cyclomaltohexaose,
cyclomaltoheptaose, and cyclomaltooctaose or α-CD, β-CD, and γ -CD [48]. These cyclomaltodextrins are formed from starch by the enzyme, cyclomaltodextrin glucanyltransferase
(CGTase). Bac. macerans CGTase primarily forms α-CD; other bacteria, for example Bac.
circulans elaborates a CGTase that primarily forms β-CD and Brevibacterium sp. elaborates
a CGTase that primarily forms γ -CD [49]. Larger cyclomaltodextrins, having 9, 10, 11, and
1.2
75
transucrase from L. mesenteroides NRRL B-512F. It has 95% α-(1→6) linkages with 5%
α-(1→3) branch linkages that have branches that are both single glucose residues and long α(1→6) linked chains and contains ∼10 6 to 10 8 D-glucopyranose residues. Other strains make
a wide variety of dextrans with various degrees of branching, not only through α-(1→3) linkages, but through α-(1→2) and/or α-(1→4) linkages as well. In some cases, the degree of
branching is as low as 3%, and in other instances, virtually every glucose residue in the backbone may be substituted with a branch linkage [41].
Some of these bacteria also elaborate glucansucrases that synthesize polysaccharides that are
not considered dextrans because they do not have contiguous α-(1→6) linked main chains.
L. mesenteroides NRRL B-1355 secretes a dextransucrase that synthesizes a B-512F-type dextran and another enzyme, alternansucrase, that synthesizes an α-glucan from sucrose that has
alternating α-(1→6) and α-(1→3) linked glucose residues in the main chains with 7–11%
α-(1→3) branch chains of alternating α-(1→6) and α-(1→3) linked glucose residues [41].
This α-glucan is called alternan. Another glucansucrase, mutansucrase, secreted by Streptococcus mutans, synthesizes a linear glucan in which the D-glucopyranose residues are linked
α-(1→3). It is particularly characterized by being extremely water-insoluble in contrast to the
dextrans and alternan that are highly water-soluble [41].
Pullulan is a polysaccharide that is elaborated by several species of the fungus, Aureobasidium, particularly A. pullulans. This fungus is typified by the presence of black pigments and
is sometimes called “black yeast” [43]. Pullulan is a water-soluble, linear polysaccharide of
D-glucopyranose residues joined together by a repeating sequence of two α-(1→4) and one
α-(1→6) linkages. The structure is that of a polymer of maltotriose units joined together end
to end by α-(1→6) linkages [44,45,46]. In addition to maltotriose units, it also has ∼5–7%
maltotetraose units located in the interior of the polysaccharide chain [47].
These bacterial polysaccharides have been considered to be “slimes”; they are often in reality
loose capsules that are produced extracellularly by the bacteria. It was found that low molecular weight L. mesenteroides NRRL B-512F dextran could be used as a blood plasma extender
and was produced on a relatively large scale during the “cold war”, but also found uses as
a gel-filtration material when cross-linked by epichlorohydrin to give a family of cross-linked
dextrans [41].
5.4 Properties and Occurrence of D-Glucose in Cyclic Dextrins
A number of different kinds of nonreducing cyclic dextrins containing D-glucopyranose
residues occur. The first to be observed were the cyclomaltodextrins (sometimes referred to
in the older literature as cyclodextrins or Schardinger dextrins), which have been known for
over 100 years. They were first found in rotting vegetables and then in the fermentation of
starch by a heat-resistant microorganism called Bacillus macerans. The compounds were
crystallized from alcohol solutions and shown to be α-(1→4) linked, nonreducing, cyclic dextrins composed of six, seven, and eight D-glucopyranose residues, named cyclomaltohexaose,
cyclomaltoheptaose, and cyclomaltooctaose or α-CD, β-CD, and γ -CD [48]. These cyclomaltodextrins are formed from starch by the enzyme, cyclomaltodextrin glucanyltransferase
(CGTase). Bac. macerans CGTase primarily forms α-CD; other bacteria, for example Bac.
circulans elaborates a CGTase that primarily forms β-CD and Brevibacterium sp. elaborates
a CGTase that primarily forms γ -CD [49]. Larger cyclomaltodextrins, having 9, 10, 11, and