A -Dextrinase

An a-dextrinase cleaves a-1,6 linkages, releasing glucose residues from branched oligosaccharides. 

This enzyme [EC 3.2.1.10] (also referred to as oUgo-1,6-glucosidase, sucrase-isomaltase, and limit dextrinase) catalyzes the hydrolysis of l,6-o -D-glucosidic linkages in isomaltose and dextrin products generated from starch and glycogen via a-amylase. See also Sucrase... 

The majority of dextrans in nature are produced extracellularly via dextran-sucrase from sucrose by several lactic acid bacteria, principally Leuconostoc and Streptococcus species [13]. Dextran is also synthesised by dextrinase of different Gluconobacter species [56]. Referring to this enzyme, fermentation of maltodextrins leads to a- —4) branched dextrans with comparatively lower Mw. However, dextransucrase from Leuconostoc mesenteroid.es NRRL B-512F has attracted most interest because of commercial use. 

The latest International Union Biochemicals report includes an enzyme 3.2.1.41 a-dextrin endo-l,6-a-glucosidase, other names limit dextrinase, amylopectin 6-glucanohydrolase, pullulanase. 

Dohlert and Knutson (1991) and D. J. Manners (personal communication) reported that extracts of sugary maize contain a mixture of limit dextrinase and isoamylase. However, James et al. (1995) reported that su 1 codes for the isoamylase. 

Dextrinases, a-glucosidases, and disaccharidases located on the surface of the brush border of the intestinal epithelial cell complete the conversion of starch to glucose. 

Broad-bean limit-dextrinase, originally termed R-enzyme, has been used for the structural analysis of a-dextrins for example, 6 -a-maltosylmalto-triose [0-a-n-glucopyranosyl-(l—>4)-0-a-D-glucopyranosyl-(l- 6)-0-a-n-... 

Furegon, L., Peruffo, A.D.B., and Curioni, A., Immobilization of rice limit dextrinase on Y-alumina beads and its possible use in starch processing, Proc. Biochem., 32, 113, 1997. 

A carbohydrase-free limit dextrinase from malted sorghum flour readily... 

Dextran-Dextrinase. A dextran-forming enzyme from Acetobacter cap-sularum converts a-1,4 linkages to a-1,6, but acts only on substrates of intermediate size. This dextran-dextrinase catalyzes a reversible reaction in which the terminal residue of either a dextrin (a-1,4) or a dextran (a-1,6) is transferred to the other polysaccharide. ... 

The results of a detailed comparison of the relative efficiencies of different procedures for solubilizing the membrane-bound a-o-glucosidases of porcine intestinal mucosa have been reported. Procedures for the selective solubilization of certain members of the complex group of a-D-glucosidases have b en developed. The selective solubilization led to the conclusion that separate a-D-glucosidases (isomaltase and limit dextrinase respectively) are involved in the hydrolysis of isomaltose and the a-limit dextrins formed from starch by a-amylase. 

GA induces de novo synthesis of proteinase, limit dextrinase, pentosanases and a-glucosidase Undisputed... 

GA—these are limit dextrinase and a-glucosidase [47]. The significance of these enzymes in the hydrolysis of starch reserves is discussed in Chapter 6. jS-Amylase is not synthesized de novo in the presence or absence of GA, but is carried over in an inactive form from the developing grain. It may be activated indirectly by GA through induction of a proteinase which releases it from its inactive bound form (Chap. 6). 

A limit dextrinase isolated from broad-bean ( Vicia fabd) flour readily hydrolysed branched a-dextrins containing maltosyl or maltotriosyl side-chains, pullulan, and amylopectin j6-limit dextrin, whereas it hydrolysed glycogen -limit dextrin and amylopectin slowly and glycogens not at all. ... 

The substrate specificities of purified limit dextrinases from ungerminated oats (Avena sativa) and rice Oryza sativd) have been compared with that of a bacterial isoamylase/ The cereal enzymes are able to hydrolyse a-(l 6)-D-glucosidic linkages in oligosaccharides, a-dextrins, pullulan, amylopectin, and the -limit dextrins of amylopectin and glycogen, but are unable to hydrolyse glycogens. 

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