Glucose debranching enzyme

P-amylase, and debranching enzymes. Conversion of D-glucose to D-fmctose is mediated by glucose isomerase, mosdy in its immobilized form in columns. Enzymic degradation of starch to symps has been well reviewed (116—118), and enzymic isomerization, especially by immobilized glucose isomerase, has been fiiUy described (119) (see Syrups). 

FIGURE 23.15 The reactions of glycogen debranching enzyme. Transfer of a group of three o -(l 4)-linked glucose residues from a limit branch to another branch is followed by cleavage of the o -(l 6) bond of the residue... 

III Cori Glycogen debranching enzyme Mild hypoglycemia, liver enlargement Short outer branches Single glucose residue at outer branch... 

Answer D. This activity of the debranching enzyme removes 1,6-linked glucose residues from the branch points during glycogenolysis. 

Amylo-l,6-Glucosidase (Debranching Enzyme, EC 3.2.1.33), Assay with [14C]-Glucose... 

Table 4.6.11 Mixtures for liquid scintillation counting of amylo-1,6-glucosidase (debranching enzyme assay with [14C]-glucose) for liver and muscle, and for RBC...

The produced glucose from phosphorylase limit dextrin is determined as a measure of the debranching enzyme activity. This assay method is used for the detection of GSD Hid, a subtype in which only the translocase activity of the enzyme (see section 4.6.17.2) is affected [9,12, 20]. 

The debranching enzyme was thought to have a single activity, the function of which was to remove the glucose stub, thus allowing phosphorylase to further attack the debranched structure. 

Figure 21. Double-reciprocal plot of Bis-Tris inhibition of debranching enzyme glucosidase activity using glucose-14C assay (39)...

The glycogen debranching enzyme is the first bifunctional eukaryotic enzyme to be reported that consists of a single polypeptide chain. It catalyzes two distinct activities an oligosaccharide frons-glycosylation followed by hydrolysis of an (1—> 6)-linked D-glucosyl unit to liberate free glucose. Physical-chemical and kinetic characterization of this novel bifunctional enzyme is described by Nelson. 

Branched cydodextrins are also used to increase the solubility of complexes. Two methods are used to make branched cydodextrins, an enzymic method and a pyrolytic method. In the enzymic method, a starch debranching enzyme, such as pul-lulanase, is added to a solution of cyclodextrin and a large excess of D-glucose or maltose to force the reaction to proceed in the reverse direction, i.e. to add rather than remove a branch.69 Since the equilibrium favors the debranching reaction, yields are low and the product typically contains —15% branched cyclodextrin and —85% glucose or maltose. Purification is difficult because of the high solubility of both the glucose or maltose and the branched cyclodextrin, but much of the unreacted cyclodextrin can be removed by crystallization. 

---