Nonreducing 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) ... 

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). 

Xanthan. Xanthan, known commercially as xanthan gum [11138-66-2], has a main chain of (1 — 4)-linked P-D-glucopyranosyl units therefore, the chemical stmeture of the main chain is identical to the stmeture of cellulose [9004-34-6]. However, in xanthan, every other P-D-glucopyranosyl unit in the main chain is substituted on 0-3 with a trisaccharide unit. The trisaccharide side chain consists of (reading from the terminal, nonreducing end in towards the main chain) a -D-mannopyranosyl unit linked (1 — 4) to a P-D-glucopyranosyluronic acid unit linked (1 — 2) to a... 

Amylases are exoen2ymes that attack amylose chains and result in the successive removal of maltose units from the nonreducing end. In the case of amylopectin, the cleaving stops two to three glucose units from the a-1,6-branching points. ( -Amylase [9000-91-3] is used for the production of maltose symps and for adjunct processing in breweries. The most important commercial products are made from barley or soybeans. 

The ABO substances have been isolated and their structures determined simphfied versions, showing only their nonreducing ends, are presented in Figure 52—6. It is important to first appreciate the structure of the H substance, since it is the precursor of both the A and B substances and is the blood group substance found in persons of type O. H substance itself is formed by the action of a fiicosyltransferase, which catalyzes the addition of the terminal fiicose in al —> 2 linkage onto the terminal Gal residue of its precursor ... 

Description glycosidic cleavage to form an oxonium ion charge retained on nonreducing end positive-ion mode only often referred to as A -type cleavage, because of similarity to one of the cleavages seen in electron impact-mass spectrometry. 

Description glycosidic cleavage with a hydrogen transfer charge retained on the nonreducing end positive- and negative-ion modes. 

Description ring cleavage charge retained on nonreducing end infrequent pathway in the positive-ion mode, but a major pathway in the negative mode, because a stable, enolate anion results from loss of the enolic hydrogen atom ions are 42 mass units higher than those formed in Pathway C. 

It is clear that the unsaturated nonreducing GalA unit must result from the cleavage by RG-lyase, since the original RGO contains a saturated GalA at the nonreducing end. The structures therefore can be positioned as follows ... 

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