Mannose in glycoproteins

The content of L-fucose and D-mannose in glycoproteins has been determined by h.p.l.c. of the perbenzoyl-D-[ H]fucitol and -D-[ H]mannitol derivatives. Since D-galactitol and D-glucitol cannot be separated from D-mannitol using this system, samples containing these polyols must be subjected to electrophoresis prior to h.p.l.c. 

The content of L-fucose and D-mannose in glycoproteins has been determined by h.p.l.c. of the perbenzoyl-L-[ H]fucitol and D-[ H]mannitol derivatives. 

Although a-D-mannosidase appears to be under endocrine control,28,28 its natural function remains obscure. It is probable that the enzyme is important in the catabolism of D-mannose-containing glycoproteins,12,16,88 and, therefore, that the important trace element zinc could be indirectly implicated in this process. It is well known that zinc deficiency has an adverse effect on fertility in the male,89,90 and it could be argued that the changes observed in a-D-mannosidase activity in uterus and epididymis indicate that this enzyme is important in reproduction. It is scarcely justifiable to ascribe a cause-and-effect relationship to the correlations observed between the zinc content and the a-D-mannosidase activity in epididymis. All that can be said with any certainty is that, under certain circumstances, the two variables respond together to a common stimulus. 

Apart from those examples discussed in which purified a-D-mannosidase was employed, numerous other studies have been made of D-mannose-containing glycoproteins by purely chemical methods for reviews, see articles by Marshall and Neuberger97 Spiro,111 and Pazur and Aronson.125... 

Mannose, the C-2 epimer of glucose (see p. 84), is an important component of glycoproteins (see p. 164). Hexokinase phosphorylates mannose, producing mannose 6-phosphate, which, in turn, is (reversibly) isomerized to fructose 6-phosphate by phosphoman-nose isomerase. [Note There is little mannose in dietary carbohydrates. Most intracellular mannose is synthesized from fructose, or is preexisting mannose produced by the degradation of structural carbohydrates and salvaged by hexokinase.]... 

The putative pathway of coordination of mannan and PolyP biosynthesis by cell-wall formation has been proposed (Kulaev, 1994), which explains the presence of PolyP outside of the cytoplasmic membrane (Figure 7.4). Dolichyl-phosphates (Dol-Ps) act as transmembrane carriers of carbohydrate residues in glycoprotein biosynthesis. GDP-mannose at the... 

N-acetylglucosamine, terminal a-N-acetyl-lactosamine and terminal N-Acetyllactosamine residues in glycoproteins Terminal mannose a(2-3)-linked sialic acid... 

Fig. 3-119. Separation of the monosaccharide components present in glycoprotein hydrolysates. — Separator column CarboPac PA-1 eluent 0.022 mol/L NaOH flow rate 1 mL/min detection pulsed amperometry at a Au working electrode after post-column addition of 0.3 mol/L NaOH injection volume 50 pL solute concentrations 2.5 nmol each of fucose (1), 2-deoxyglucose (2), galactosamine (3), glucosamine (4), galactose (5), glucose (6), and mannose (7) (taken from [111]).

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