Curdlan conformational transition

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. 

Observation of the dependence of the absorption maximum of Congo red in the presence of curdlan on the alkali concentration showed that at low NaOH concentrations signiftcant shift to the longer wave-lengths occurred. The concentration interval in which the conformational transition took place was also the region where the abrupt decrease of the Congo red absorption maximum occurred [66]. 

C. Conformational Transition Figure 7 shows that the C NMR spectra of curdlan in the presence of dilute alkali up to 0.19M are essentially the same as those of the elastic gel (6). Therefore, molecular organization of the curdlan sample in dilute alkaline state is essentially the same as that of the elastic gel. 

Scleroglucan exists in a triple hehcal conformation that is highly stable (314). The D-glucopyranosyl side groups project to the outside of the helix (312) and prevent the aggregation of hehces, which would result in insolubiUty, as in the case of curdlan vide infra). The transition from helix to coil occurs... 

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