Hexose components

Extrafloral nectaries include a wide range of nectar-excreting structures, which are distinguished from their floral counterparts by the fact that they are not involved in pollination. Extrafloral nectar is typically dominated by sucrose and its hexose components glucose and fructose. The fact that these common sugars are acceptable to the majority of insects, combined with the exposed nature of extrafloral nectaries, makes them suitable food sources for abroad range of insects. Compared with floral nectar, extrafloral nectar often has increased fructose and glucose levels (Tanowitz... 

Hexose Components of Bacterial Polysaccharides Having a Configuration Different from... 

Sucrose is probably the most abundantly produced bulk chemical. It can be degraded to its hexose component sugars D-glucose and D-fructose. 

Pyrophosphate Uridyl Transferase. The over-all epimerase reaction is composed of three individual reactions. The sugar phosphates are not converted directly into each other, but are first incorporated into uridine nucleotides. Epimerization occurs in the hexose component of the UDP-sugar, which then is cleaved to yield the epimerized sugar phosphate. The synthesis of both UDPG and the corresponding galactose derivative, UDPGal, are catalyzed by enzymes called uridyl transferases. A pyrophosphate (PP) uridyl transferase has been studied in yeast and in several mammalian tissues. It catalyzes the reaction... 

Brante, G. Studies on the lipids in morbus Gaucher. I. Qualitative and quantitative determination of the hexose components in normal and Gaucher glycolipids. Acta Soc. Med. upsalien. 56, 125 (1951). 

The structure (336) of the octasaccharide antibiotic eveminomycin D produced by Micromonospora carbonaceae has been reported by Ganguly and his coworkers. Orthoester linkages akin to that present in eveminomycin D are also found in destomycins A, B, and C, which chemical and spectroscopic evidence indicated to have the structures (337) each antibiotic contains a 6-amino-6-deoxyheptopyranosylidene residue attached to a D-hexose residue, which is linked in turn to streptamine. o-Talose is the hexose component of destomycins A and C. 

Several features of the rearrangement have been elucidated. Although in the treatment of the ester 26 with acetic acid the products were isolated in only 64% yield, evidence was obtained (22) that finally no 1,2-unsaturated compounds remained, since the noncrystalline portion on hydrogenation and deacetylation afforded only 3-deoxy-D-ribo and -d-arabino-hexose and no 1,5-anhydrohexitols. That the components of the final mixture were in equilibrium was indicated by the observation that the main component 27 underwent reaction in boiling acetic acid to give a solution with the same optical activity as that of the original reaction mixture. Thus the 2,3-unsaturated compounds are more stable than the hydroxyglycal derivatives and the a isomer 27 is more stable than its anomer 28. 

Pyruvate ketals add to the anionic nature of the exopolysaccharide and are usually present in stoichiometric ratios with the carbohydrate component Pyruvate is normally attached to the neutral hexoses but may also be attached to uronic adds. In the absence of uronic acids, pyruvate alone contributes to the anionic nature of the exopolysaccharide. 

The introduction of the invertase from yeast alone was not sufficient. Invertase cleaves sucrose to release the two component sugars, glucose and fructose. While fructose can be readily metabolized by fructokinase in potato tubers, there is insufficient hexokinase activity in developing potato tubers to bring the glucose into intermediary metabolism. Therefore, it was necessary to introduce a second transgene, a bacterial glucokinase, in order to ensure that the hexoses became available for subsequent metabolism.25... 

Diisobutylaluminum hydride was also employed (153) for the reduction of 2,6-dideoxy-3-C-methyl-D-arabmo-hexono-1,4-lactone (121) to an antibiotic component, the branched-chain sugar evermicose (2,6-dideoxy-3-C-methyl-D-nrabmo-hexose, 122). The L-enantiomer of 122 (olivomycose, 125a), L-amicetose 125b, and 2,6-dideoxy-3-C-methyl-L-n Zw-hexose (l-... 

Figure 9.12 Deoxy derivatives. These contain one less oxygen atom than the monosaccharide from which they are derived. 2-Deoxyribose is a most important deoxy pentose and is a major constituent of deoxyribonucleic acid (DNA). Deoxy hexoses are widely distributed among plants, animals and microorganisms especially as components of complex polysaccharides. Examples are rhamnose (6-deoxymannose), a component of bacterial cell walls, and fucose (6-deoxygalactose), which is often found in glycoproteins and is an important constituent of human blood group substances.

Two other commonly occurring hexoses which are usually found as components of polysaccharides or combined with other molecules in complex structures are galactose and fructose and, in a similar manner to other monosaccharides, enzymic methods are available for their measurement. An enzymic method for the measurement of fructose using hexokinase was described earlier, together with the method for mannose and glucose (Figure 9.22). 

---