88] Enzymes of glycogen debranching: Amylo-1,6-glucosidase (I) and oligo-1,4→1,4-glucantransferase (II)

Abstract

This chapter describes the specific oligosaccharide substrates for the separate measurement of each enzymatic activity (I and II). The nature of the reaction catalyzed by II is demonstrated using these substrates. Enzymes I and II act with phosphorylase to bring about the total degradation of glycogen to glucose 1-phosphate and glucose. The amylo-l,6-glucosidase appears to act directly on a polysaccharide limit dextrin to form glucose from its outermost branch points. The separate activity of amylo-l,6-glucosidase (I) is measured with certainty only when the substrate used is a branched oligosaccharide with the general structural features of B5. A limit dextrin (LD) of glycogen may not be a specific substrate for (I), as the number of exposed branch point glucose residues in the LD is not known with certainty. The initial rate of glucose formation from an LD may depend only on the action of (I) and be independent of the prior action of (II). The enzymatic activity of Oligo-l,4 → 1,4-glucantransferase (II) consists of the transfer of terminal maltosyl and, to a greater extent, maltotriosyl residues from α-l,4-1inkage in one chain to α-l,4-1inkage in another. The reagents used, procedure followed, and the steps involved in the purification are also described in the chapter.