Hexosamine structure

Microorganisms show a mucli greater profusion of hexosamine structures than those described from other sources. This is particularly true of hexosamines present in antibiotics (Dutcher, 1963). 

The widespread distribution of D-giucosamine (I) and n-galactosamine (II) is presumably due to the closeness of the metabolic relationship between these hexosamines (Davidson, 1966) and the ubiquitous, and thermodynamically most stable hexose, n-glucose. While it is possible that some of the other hexosamine structures listed in Table I have yet to be detected as natural components in materials of animal origin, it is unlikely that such sources would match the diversity of hexosamine structures exhibited in compounds from microoi anisms. 

Properties and Structure. a -Acid glycoprotein (a -AGP) has a molecular mass of about 41,000 and consists of a peptide chain having 181 amino acid residues and five carbohydrate units (14,15). Two cystine disulfide cross-linkages connect residues 5 and 147 and residues 72 and 164. The carbohydrate units comprise 45% of the molecule and contain siaUc acid, hexosamine, and neutral hexoses. In phosphate buffer the isoelectric point of the... 

Both positional linkages (uronic acid to hexosamine and hexosamine to uronic acid) were established as being (1 — 4) by structural analysis of the previously mentioned (see Section IV), crystalline disaccharides containing D-glucuronic acid, isolated from an acid hydrolyzate of carboxyl-reduced heparin.128-129 Further evidence was obtained from the structure of the D-glucuronic acid-containing counterpart of disaccharides 6 and 8, obtained as minor products from pig-mucosal heparin following nitrous acid deamination,1110 136-138 and acid hydrolysis followed by N-acetylation,130 respectively. 

Type IV Pneumococcus Specific Polysaccharide.—This capsular material110 ([ck]d + 33°, water) has been hydrolyzed and shown to contain units of D-glucose and N-acetyl-hexosamine. Its structure has not yet been studied. 

The structural components encountered in E. coli are also present in lipid A of other bacterial sources. Thus, a survey of the structures analyzed shows that lipid A, in general, contain two g/wcoconfigured and pyranosidic D-hexosamine residues (2-amino-2-deoxy-D-glucose, GlcpN, or 2,3-diamino-2,3-dideoxy-D-glucose, GlcpN3N, also termed DAG (49,50)], which are present as a ) -(l — 6)-linked disaccharide (monosaccharide backbones have also been identified, but the respective lipid A lack endotoxic activity). The disaccharide is phosphorylated by one or, in most cases, two phosphate... 

Results of an experiment with an oligosaccharide free from amino acid were less conclusive, but were not incompatible with the structure shown. The oligosaccharide was prepared from a separated glycoprotein fraction having a D-mannose hexosamine ratio of 5 3. a-D-Mannosidase and 2-acetamido-2-deoxy-/3-D-glucosidase were used alternately. Initially, a-D-mannosidase removed about 1.5 D-mannose residues per molecule. Subsequent treatment of the residual oligosaccharide with 2-acetamido-2-deoxy-/3-D-glucosidase released rather less than one proportion of hexosamine residue, and then another 1.5 residues of D-mannose became open to attack by a-D-mannosidase. 

R. Montgomery and his colleagues108 fractionated, on Dowex 50, the aspartamidoglycan from ovalbumin. The five components obtained were each subjected to exhaustive hydrolysis with a-D-man-nosidase and 2-acetamido-2-deoxy-/3-D-glucosidase, used separately. The results are shown in Table X. One way in which to explain these results would be to change the position of the extra hexosamine residue in 1, to give the alternative structure 2. 

Further evidence for the presence of /8-D-linked D-mannose in the inner core of ovalbumin was provided by the results obtained on use of purified enzymes from hen oviduct.20 a-D-Mannosidase released four residues of D-mannose from the molecule of a glycopeptide having D-mannose hexosamine L-asparagine ratios of 5 2 1, whereas /3-D-mannosidase had no effect thereon. /3-D-Mannosidase did, however, remove the remaining D-mannose residue. It would appear that the resistant core has structure 3. 

A slightly larger fragment containing five D-mannose and two hexosamine residues per molecule seems to be common to all of the glycopeptides that have been isolated from ovalbumin. A useful step forward would be to ascertain whether this fragment has an invariant structure. 

Cornforth, J.W. and Firth, M.E. 1958. Identification of two chromogens in the Elson-Morgan determination of hexosamines. A new synthesis of 3-methylpyrrole. Structure of the pyrolene-phthalides . J. Chem. Soc. 1091-1099. 

The data presented in this report allow the assignment of partial structures for four neutral glycosphingolipids of human neutrophils Hexose-O-Cer, Hexose-Q-Hexose-O-Cer, Hexosamine -0-Hexose-0-Hexose-0-Cer and Hexose-O-Hexosamine-O-Hexose-0-Hexose-0-Cer. 

Disaccharides of the hexuronic acid-hexosamine type constitute the fundamental repeating unit of many mucopolysaccharides, from which they are derived by hydrolytic degradation. Further hydrolytic treatment results generally in destruction of the uronic acid moiety of the disaccharide. Structural studies have been made on the disaccharides from hyaluronic acid (hyalobiouronic acid), chondroitinsulfate (chondrosine), and heparin (heparosine). 

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