Curdlan 1 3 glucan

Single linkage type. Several of these are neutral glucans, eg curdlan. Others are polyanionic homopolymers and, unlike the glucans, also contain acyl groups. 

Another promising exopolysaccharide that may come to replace some of the traditional setting agents is curdlan. This is an a-1,3 linked glucan made by Alcaligenes faecalis which retains its shape in cooked food and only needs temperatures of between 55 and 80°C for preparation. 

Curdlan possesses anti-tumour activity similar to that shown by fungal (1-D-glucans, a property which appears to be related to the ability to form triple helices. 

Consistent with the above observations, the immunoactive glucans such as curdlan (9), lentinan (10), scleroglucan (11), schizophyllan (12) and yeast glucan (13) share a common p-D(l-3)-linked glucopyronosyl backbone. Some of these polymers also contain p-D(l-6)-linked glucopyranosyl branches through the 3,6-di-O-substituted C-6 atom of the backbone residues. 

Figure 2 compares the conformational transition curves of wild-type yeast glucan (branch frequency = 0.20) and PGG (branch frequency = 0.50). Wild-type yeast glucan required approximately 0.1M NaOH to disrupt the triple helical conformation, whereas this transition is observed at approximately 0.04 M NaOH with PGG. This trend is consistent with the observation that curdlan, an entirely linear p-D(l-3)-linked glucan, requires approximately 0.25M NaOH to disrupt the ordered conformation (76). Hence, it is concluded that the highly branched PGG molecules only form weak inter-chain associations resulting in the formation of predominantly single-helical zones. 

Figure 2 Effect of branch frequency on glucan conformation. Conformational characterization of glucans was carried out as described in the experimental section. Curdlan is a linear p(l-3)linked glucan Yeast glucan has a 30% P(l-6) branch frequency and PGG-R glucan has a 50% p(l-6) branch frequency. The Congo Red-single/triple helix complex absorption maxima are indicated.

Figure 17 Schematic representation of heterogeneous portions of curdlan hydrogel (left) (A) liquid-like portion, (B) portion of intermediate mobility, and (C) triple-helical cross-links in the solid-like portion and crystallites as additional cross-links, and branched glucans (triple helical chains) (right). From Ref. 117 with permission.

The change of the crystal structure of (l- -3)-a-D-glucan should be compared to the case of (l- -3)-3-D-glucan (curdlan). Although curdlan changes its polymorphic form by annealing (6), neither the fiber patterns (samples B and C) nor the powder patterns (samples A and D) underwent polymorphic transformations due to annealing. 

C3K produces an insoluble exocellular polysaccharide(1). This polysaccharide is entirely composed of D-glucosyl residues which are connected almost exclusively by B-(l- -3)-linkages. This and the similar glucan formed by some strains of Agrobaoterium are named Curdlan because they form irreversibly, resilient gel when heated in water. 

The extracellular microbial polysaccharide curdlan is essentially a linear homopolymer of 6-(l-3)-D-glucan as illustrated in Figure 1. It is produced from the mutant strain of the bacteria Alcaligenis faecalis and was first isolated and investigated by Harada and coworkers (J -3) who coined the name curdlan to describe the gelling behaviour of the polysaccharide at elevated temperatures. 

Curdlan adopts a triple helix conformation in the dispersed and solid states (Deslandes et al., 1980) and reverts to a random coil in 0.25-M sodium hydroxide (Stipanovic and Giammatteo, 1989). Some glucans are ordered in dilute alkali and disordered at higher concentrations (Ogawa et al., 1972). 

Nakanishi, I., Kimura, K., Kusui, S., and Yamazaki, E. (1974). Complex formation of gel-forming bacterial (l,3)-P-D-glucans (curdlan-type polysaccharides) with dyes in aqueous solution. Carbohydr. Res. 32 47-52. 

Curdlan is a bacterial polysaccharide made by Agrobacterium biovar [87,88,89]. It is a linear (1 3)- -glucan (MW 73,000) that forms a triple helix. Curdlan is insoluble in cold water. When aqueous dispersions of curdlan are heated, two types of gels form. First curdlan dissolves. When the solution reaches 55-66 °C, then is cooled, a reversible gel forms. The gel melts when held at about 60 °C. When the thermoreversible gel is heated to a temperature above 80 °C, an irreversible gel forms. Heating to higher temperatures results in stronger irreversible gels. Transition temperatures are a function of concentration. 

Curdlan, which is a linear (1—> 3)-/3-D-glucan (O Scheme i), also suppresses the proliferation of subcutaneously implanted sarcoma 180 markedly [7]. Curdlan sulfate with a high degree of suhstitution (O Scheme 4) is reported to exert strong anti-human immunodeficiency virus (anti-HIV) activity [8,9]. 

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