76
1
General Principles
12 D-glucopyranose residues were later obtained in relatively small quantities, and even later,
cyclomaltodextrins having as many as 25 glucose residues were obtained [50]. The internal
cavity of the cyclomaltodextrins is relatively hydrophobic, giving them the property of forming
complexes with a wide variety of organic molecules [51].
Cycloisomaltodextrins, linked α-(1→6) containing seven, eight, and nine D-glucopyranose
residues have been found to be formed by a bacterial cycloisomaltodextrin dextran-glucanyltransferase, acting on B-512F dextran [52]. A cyclic tetrasaccharide, containing four glucose residues with alternating α-(1→6) and α-(1→3) linkages has been obtained from the
reaction of a bacterial enzyme on alternan [53]. This enzyme, 3-α-isomaltosyltransferase, is
part of a 2-enzyme system that converts starch to the cyclic tetrasaccharide [54,55]. Also,
Bacillus stearothermophilus starch branching enzyme catalyzed a reaction with amylose to
give macrocyclic dextrins with one α-(1→6) linkage at the site of transglycosylation coupling [56].
Another group of cyclic dextrins is the cyclosophorans, which consist of 17–40 D-glucopyranose residues linked β-(1→2). They are produced by Rhizobium species involved in nitrogenfixing nodules on the roots of legumes [59] and are also found in plant crown galls, produced
by Agrobacterium tumefaciens [58]. The sizes of the cyclosophorans vary depending on the
particular species of Rhizobium, which are also specific for the particular type of legume that
they associate with to form the nodules. There is some evidence that the cyclosophorans play
a role in the formation of the nodules and the crown galls [59].
Bradyrhizobium species synthesize a related cyclic dextrin that contains 12 D-glucopyranose
residues linked by a repeating sequence of three contiguous β-(1→6) linkages followed by
three contiguous β-(1→3) linkages. One of the β-(1→3) sequences has a single branched
D-glucopyranose residue substituted β-(1→6) onto the center D-glucopyranose residue [60].
A cyclodextrin containing only β-(1→3) linkages (cyclolaminarinose) has been found to be
elaborated by a recombinant strain of Rhizobium meliloti TY7 mutant that is deficient in forming cyclosophoran, but carrying the genetic locus of Bradyrhizobium japonicum USDA 110.
The cyclolaminarinose dextrin has 10 D-glucopyranose residues, with a single laminaribiose
disaccharide substituted β-(1→6) onto the ring [61].
5.5 Properties and Occurrence of Cellulose
Cellulose is usually considered the most abundant carbohydrate on the earth, occurring in all
plant cell walls to the extent of approximately 50% by weight; 20–40% of the cell wall is
made up of hemicelluloses, and the remaining 10–30% is the noncarbohydrate, lignin, which
acts as a cross-linking and cementing agent in the plant cell wall, covalently attached to the
hemicelluloses [62]. Hemicelluloses are a family of polysaccharides, with a structure similar
to cellulose, but besides D-glucopyranose residues, they contain several other monosaccharide residues, such as D-xylopyranose, D-mannopyranose, D-galactopyranose, D-glucopyranose uronic acid, and L-arabinofuranose residues (see > Sect. 6).
Cellulose is a very large, linear polysaccharide of ∼10 6 to 10 8 D-glucopyranose residues,
linked β-(1→4) to each other. Because of its high water-insolubility, its actual size has never
been accurately determined. It is a β-glucan with a very tight helical structure in which the
individual glucose residues are oriented 180°to each other [63]. Because of this conformation and the β-linkages, cellulose chains readily form intermolecular hydrogen bonds, giving
1
General Principles
12 D-glucopyranose residues were later obtained in relatively small quantities, and even later,
cyclomaltodextrins having as many as 25 glucose residues were obtained [50]. The internal
cavity of the cyclomaltodextrins is relatively hydrophobic, giving them the property of forming
complexes with a wide variety of organic molecules [51].
Cycloisomaltodextrins, linked α-(1→6) containing seven, eight, and nine D-glucopyranose
residues have been found to be formed by a bacterial cycloisomaltodextrin dextran-glucanyltransferase, acting on B-512F dextran [52]. A cyclic tetrasaccharide, containing four glucose residues with alternating α-(1→6) and α-(1→3) linkages has been obtained from the
reaction of a bacterial enzyme on alternan [53]. This enzyme, 3-α-isomaltosyltransferase, is
part of a 2-enzyme system that converts starch to the cyclic tetrasaccharide [54,55]. Also,
Bacillus stearothermophilus starch branching enzyme catalyzed a reaction with amylose to
give macrocyclic dextrins with one α-(1→6) linkage at the site of transglycosylation coupling [56].
Another group of cyclic dextrins is the cyclosophorans, which consist of 17–40 D-glucopyranose residues linked β-(1→2). They are produced by Rhizobium species involved in nitrogenfixing nodules on the roots of legumes [59] and are also found in plant crown galls, produced
by Agrobacterium tumefaciens [58]. The sizes of the cyclosophorans vary depending on the
particular species of Rhizobium, which are also specific for the particular type of legume that
they associate with to form the nodules. There is some evidence that the cyclosophorans play
a role in the formation of the nodules and the crown galls [59].
Bradyrhizobium species synthesize a related cyclic dextrin that contains 12 D-glucopyranose
residues linked by a repeating sequence of three contiguous β-(1→6) linkages followed by
three contiguous β-(1→3) linkages. One of the β-(1→3) sequences has a single branched
D-glucopyranose residue substituted β-(1→6) onto the center D-glucopyranose residue [60].
A cyclodextrin containing only β-(1→3) linkages (cyclolaminarinose) has been found to be
elaborated by a recombinant strain of Rhizobium meliloti TY7 mutant that is deficient in forming cyclosophoran, but carrying the genetic locus of Bradyrhizobium japonicum USDA 110.
The cyclolaminarinose dextrin has 10 D-glucopyranose residues, with a single laminaribiose
disaccharide substituted β-(1→6) onto the ring [61].
5.5 Properties and Occurrence of Cellulose
Cellulose is usually considered the most abundant carbohydrate on the earth, occurring in all
plant cell walls to the extent of approximately 50% by weight; 20–40% of the cell wall is
made up of hemicelluloses, and the remaining 10–30% is the noncarbohydrate, lignin, which
acts as a cross-linking and cementing agent in the plant cell wall, covalently attached to the
hemicelluloses [62]. Hemicelluloses are a family of polysaccharides, with a structure similar
to cellulose, but besides D-glucopyranose residues, they contain several other monosaccharide residues, such as D-xylopyranose, D-mannopyranose, D-galactopyranose, D-glucopyranose uronic acid, and L-arabinofuranose residues (see > Sect. 6).
Cellulose is a very large, linear polysaccharide of ∼10 6 to 10 8 D-glucopyranose residues,
linked β-(1→4) to each other. Because of its high water-insolubility, its actual size has never
been accurately determined. It is a β-glucan with a very tight helical structure in which the
individual glucose residues are oriented 180°to each other [63]. Because of this conformation and the β-linkages, cellulose chains readily form intermolecular hydrogen bonds, giving