Yeast debranching enzymes

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... 

Yeast Glucan Debranching Enzymes. Rombouts and Phaff (95) postulated that the lytic / -( - 6)-glucanase which they purified from... 

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. 

Another debranching enzyme, R-enzyme, bearing a resemblance to Cori s amylo-l,6-glucosidase, was shown to be present by Hobson et in the bean and potato. This enzyme likewise hydrolyzes 1,6-linkages in amylopectin but has no action on the 1,4-linkages of either amylopectin or amylose. The R-enzyme does not synthesize 1,6- or 1,4-linkages its action is purely hydrolytic. A similar debranching enzyme has also been reported in yeast by Maruo and Kobayashi and by Petrova in muscle. ... 

This procedure is not subject to any of the criticisms resulting from incorrect assumptions regarding the mechanism of debranching or the structure of the phosphorylase limit-dextrin discussed previously, and it has been used routinely with successful results. A deterrent to the use of the procedure is that it requires two purified enzymes, both of which are rather difiBcult to obtain (particularly, free from branching enzyme, which would interfere with the results). Carter and Lee used the same method with yeast glucosidase-transferase instead of muscle glucosidase-transferase. 

Kobayashi may be identical with this debranching R enzyme. In addition to these amylases acting on the 1,6 -a-glucosidic links of amylopectin there also exist amylo-1,6-glucosidases which hydrolyze the same bonds in limit dextrins of branched polysaccharides treated with jS-amylase. An amylo-1,6-glucosidase occurs in yeast and in barley malt. It is evident that crude diastase preparations may contain varying quantities of the enzymes involved in the scission of l,6 -a-glucosidic links. For this reason the purest enzymes available should be used for the determination of the end products of amylase activity. 

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