Glucans branched-chain

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. 

A mutant of starch synthase II has also been isolated in C. reinhardtiL This mutant, st-3, accumulated only 20-40% of amount of starch present in wild type. The enzyme lacking in the mutant was SSII, one of the two starch synthase isoforms present in C. reinhardtii There was also an apparent increase in the amyiose content as well as a modified form of amylopectin. The changes noted in the mutant amylopectin were, a decrease in the number of intermediate glucose branch chains of 8-50 glucose units and an increase in short-chain glucans (2—7 glucose units). The conclusion made was that this SSII was responsible for synthesis of intermediate size branch chains, a similar conclusion reached as indicated above with the function of SSII and SSIIa in higher plants. The SSII of Chlamydomonas is now referred to as SSIII. ... 

FIGURE 16.1 Preparative SEC of short-chain (scb) branched glucans of small" (<3S /u.m) starch granules of potato species Ostara separated on Sephacryl S-1000 (88 X 2.6 cm) eluent 0.005 M NaOH the normalized chromatogram (area = 1.0) was constructed from an off-line determined carbohydrate content of succeeding 5-ml fractions flow rate 0.67 ml/mln V d = 185 ml, V, = 460 ml fraction I high dp fraction fraction 2 low dp fraction. 

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