Debranching deficiency

In glycogenosis type III (debranching enzyme deficiency) the absorption maximum is around 410 nm in muscle in liver the maximum remains around 460 nm, but there is a pronounced shoulder at 410 nm. In glycogenosis type IV (branching enzyme deficiency) the absorption maximum is around 530 nm. 

Pan, D., and Nelson, O. E. 1984. A debranching enzyme deficiency in endosperms of the sugary 1 mutants of maize. Plant PhysioL 74,324-328. 

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. 

GSD type III, Cori s disease Deficiency of debranching enzyme activity causes accumulation of limit dextrins. See text. 

To explain the variation in the phosphate content of starches, it is postulated that some plants contain a specific phosphatase such an enzyme would have to possess unusual powers of penetration, since R-en-zyme, for example, cannot attack the interior of an amylopectin molecule. Moreover, a considerable proportion of the phosphorus would be situated in outer chains there is no evidence for this. (5) The formation of waxy-type starches is attributed to a low activity of the debranching enzyme caused by the presence of an inhibitor(s) to the debranching mechanism or by a deficiency of the debranching enzyme. Waxy-type starches should, therefore, contain a higher degree of branching than that actually observed (about 5%). 

Several types of glycogen-storage disease are now known in most cases, the accumulation of glycogen can be correlated with a relative deficiency of either n-glucose 6-phosphatase or the debranching-enzyme system (Type I and III disease, respectively). In a very few cases, the enzymic defect is either in branching enzyme or in phosphorylase (Type IV or VI disease, respectively) see Table VII. In the Type II and V diseases, the enzyme deficiencies are different from the above, but have not yet been fully identified. 

---