Enzymes, branching debranching

R-Enzyme was first isolated from broad beans and potatoes by Peat and coworkers. Purification was difficult in view of the relatively small amounts present and the large number of contaminating enzymes, particularly a maltodextrinyl transferase (D-enzyme), branching (Q-) enzyme, and alpha-amylase. However, a procedure was developed that gave preparations suflBciently pure to permit routine use of this enzyme during some ten years for debranching of amylaceous polysaccharides. ... 

This is due to the deficiency of the enzyme amylo-1,6-glucosidase, the enzyme which debranches glycogen. As a result, a glycogen having abnormally short branches accumulates in the tissues. 

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... 

Type III Limit dextrinosis, Forbes or Corl s disease Absence of debranching enzyme Accumulation of a characteristic branched polysaccharide. 

Debranching enzyme hydrolyzes the a1,4-bond nearest the branch point as shown. 

Debranching enzyme deconstructs the branches in glycogen that have been exposed by glycogen phosphorylase. The two-step process by which this occurs is diagrammed in Figure 1-14-4. Debranching enzyme ... 

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. 

Figure 6-5. Glycogenolysis. Degradation of glycogen occurs stepwise by hydrolysis of one glucosyl unit at a time from the nonreducing ends by phosphorylase. The limit dextrin occurs as indicated in the second step when there are four glucosyl units remaining to a branch point. Once debranching enzyme has resolved the limit dextrin, degradation by phosphorylase can resume.

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. 

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