Isoamylase plant

As noted in Section 4.3 (see also Chapter 3), a sul mutation in maize that causes a deficiency of isoamylase, an enzyme normally considered to be mainly involved in starch degradation in plants and in C. reinhadtii, results in accumulation of a water-soluble polysaccharide, phytoglycogen, instead of starch.45 19,291 In C. reinhardtii, the mutation results in complete loss of starch, but in higher plants, the lower amount of amylopectin seen in the mutant plant may be related to the severity of the enzyme deficiency.292,293... 

The branching enzyme from Bacillus stearomophilus decreased the molecular size of synthetic amylose. On studying the product of this reaction, it was found that BE had catalyzed the intramolecular transglycosylation to form a cyclic structure with a side chain. After removing the cyclic part of the molecule (using isoamylase) from the rest of the molecule, its cyclic nature was confirmed by the use of mass spectrometry. The authors proposed a new mechanism for the action of BE and suggested that plant BE may catalyze the cyclization of amylose and amylopectin. 

Posewitz, M.C., Smolinski, S.L, Kanakagiri, S., Melis, A., Seibert, M. and Ghirardi, M.L. 2004b. Hydrogen photoproduction is attenuated by disruption of an isoamylase gene in Chlamydomonas reinhardtii. Plant Cell 16, 2151-2163. 

A debranching enzyme called isoamylase is involved in synthesis of the starch granule and its polysaccharide components (34-37). Mutant plants deficient in isoamylase activity accumulate a soluble a-glucan designated phytoglycogen (3, 37, 38) and little starch. 

Isoamylases that exclusively hydrolyze the q -(1—>6) branch linkages of starch were first recognized in plants and first isolated from broad beans [92]. A bacterial isoamylase was obtained from the culturing of Pseudomonas amyloderamosa [93,94,95,96] and has found wide use in studying the structure of amylopectin and related polysaccharides [97]. 

Kubo, A, N Fujita, K Harada, T Matsuda, H Satoh and Y Nakamura (1999). The starchdebranching enzymes isoamylase and pullulanase are both involved in amylopectin biosynthesis in rice endosperm. Plant Physiology, 121, 399-409. 

Isoamylase. We have not yet mentioned enzymes that are capable of splitting a-glycosidic 1-6 linkages. These enzymes are the isoamylases. They have been detected many times in higher plants. 

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