Enzymes, debranching

GLYCINE REDUCTASE GLYCINE SYNTHASE Glycogen debranching enzyme, DEBRANCHING ENZYME Glycogenolysis tracer kinetics,... 

Liver and muscle debranching enzyme debranching enzyme in liver (normal muscle debrancher activity)... 

Another enzyme, debranching enzyme, is also involved in synthesis of the starch granule and its polysaccharide components amylose and amylopectin and this will be discussed in Section 6.15.11.1. 

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... 

The glycogen phosphorylase reaction degrades glycogen to produce limit dextrins, which are further degraded by debranching enzyme, as already described. 

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

Tabata, S. and Dohi, Y., An assay for oligo-(l—>4) —5(1—>4)-glucantransferase activity in the glycogen debranching enzyme system by using HPLC with a pulsed amperometric detector, Carb. Res., 230,179, 1992. 

Amylo-1 —> 6-glucosidase obtained by Cori and Larner218 from rabbit muscles, and R-enzyme isolated by Hobson, Whelan and Peat219 from potatoes and broad beans, are typical debranching enzymes, which will hydrolyze the 6 — 1-a-D-glucosidic linkage rather than the normal 4 —> 1-a-D linkage. These enzymes will therefore be particularly important in determinations of the fine structure of amylopectin, if they can be sufficiently well purified. 

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