Isoamylase yeast

A starch-debranching isoamylase, obtained from sugary 1 (sul) maize, has been cloned by James et al.70 and found to have 32% sequence identity with Pseudomonas isoamylase. Other isoamylases or starch debranching enzymes have been isolated from Cytophaga sp.,71 Streptomyces sp.,72 Flavobacterium sp.,73 a yeast, Lipomyces kononenkoae,74 potato tubers,75 B. circulans76 and an alkaline isoamylase with a pH optimum of 9 from an alkalophilic Bacillus sp.77... 

Since treatment of various samples of amylose with yeast isoamylase (see p. 427) caused a significant decrease in specific viscosity and a corresponding increase in / -amylolysis limit, it seems probable that some amylose molecules have a low degree of branching, and that the inter-chain linkages are of the a-D-(l—>6)-glucosidic type, as in amylopectin. However, all samples of amylose do not contain barriers to 3-amylolysis, as shown by the isolation of amylose of molecular weight 2 X 10 and /3-amylolysis limit 95% by dispersion of starch in dimethyl sulfoxide. ... 

However, evidence in favor of a true structural feature that resists the action of fcefa-amylase has come from studies of the action of debranching enzymes on amylose and its hefa-limit dextrin. Thus, by treatment with yeast isoamylase, the befa-amylolysis limit of a sample of amylose was increased from 76 to 90 , and that of amylose 6e a-limit dextrin from 6 to 77 . Treatment of amylose with pullulanase also increases the conversion of the substrate into maltose by befa-amylase to an almost quantitative value. " On the basis of these results, the anomalous linkages in amylose that resist beto-amylase action are considered to be a very small proportion of (l->6)-a-D-glucosidic linkages. 

E. C. 3.2.1.68) hydrolizes the a-l->6 links of - amylopectin, 6-limit dextrins and glycogen. Isoamylases cannot splitt the linkages of pullulans. The action is further limited by a minimum of three a-D-glucopyranosyl residues. Isoamylase is best suited for the splitting of high molecular weight starch polysaccharides. The enzyme ist produced by yeast and fungi. Optima pH 5-6.4 40° -60 °C. 

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