Reducing end

PuUulan [9057-02-7] first described in detail in 1959, is a water-soluble extracellular a-D-glucan elaborated by the fungus yiureobasidiumpullulans (formerly Eullulariapullulans) (285). It is a linear polymer of maltotriose units linked from the reducing end of one trisaccharidic unit to the nonreducing end of the next trisaccharidic unit by a(l — 6) linkages (286) ... 

The reducing-end units (see Fig. 8) are highly labile in alkaline solutions. After an initial attack by hydroxide ions at the hemiacetal function, C-1, a series of enoHzations and rearrangements leads to deoxy acids, ie, saccharinic acids, and fragmentation. Substituents on one or more hydroxyl groups influence the direction, rate, and products of reaction. 

Amylase occurs in many plants, such as barley, wheat, rye, soy beans, and potatoes, where it is generally accompanied by some a-amylase. [ -Amylase initiates hydrolysis at the nonreducing end of an amylose or amylopectin chain, and removes maltose units successively until the reducing end of the molecule is encountered in amylose or a branch is met in amylopectin. ( -Amylase is used commercially in the preparation of maltose symps. After P-amylase hydrolysis of amylopectin there remains a P-amylase limit dextrin. ( -Amylase has been used as a probe of the fine stmcture of amylopectin (43-46). 

Contains a few long-chain branches. Some chains are terminated at the reducing end with a second type of unit. 

Fig. 38.—Stereo view of three turns of the 2-fold galactomannan (45) helix containing galactose side-chains on alternate mannose residues. In this conformation, the side chains are turned up toward the non-reducing end, and the backbone is stabilized by intrachain hydrogen bonds. The helix axis is represented by the vertical line.

Description glycosidic cleavage with a hydrogen transfer charge retained on reducing end positive- and negative-ion modes often referred to as )S-cleavage. 

Table I lists the bond cleavage frequencies for PGII. G4 is exclusively split in 1-3 mode while reduced G4 was not hydrolysed. G5 is cleaved in the 1-4 and 2-3 mode at 67 % and 33 % respectively, while reduced G5 is only split into reduced G2 and G3. The reduced G6 is not cleaved in the 1-5 mode, while reduced G2 and reduced G3 are readily formed. The non-reduced G6 is cleaved in 1-5, 2-4 and 3-3 modes yielding equimolar product pairs as was also seen for the cleavage of G4 and G5. These data demonstrate that cleavage of the glycosidic bond occurs from the reducing end.

Table III. Subsite affinities At for PGII (i denotes the subsite number). Subsites with a prefix are located towards the non-reducing end of the substrate while subsites with a + prefix are located towards the reducing end. The active site is located between subsites -1 and +1. Subsites -3 to -1-1 were determined as one value.

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