Monosaccharides, reaction with protein

If not utilized in the pulp industry, hemicelluloses are hydrolyzed in the acid-catalyzed process, mainly to monosaccharides and to furan-2-aldehyde (pen-tosanes) and 5-hydroxymethylfuran-2-aldehyde (5.62) (hexosanes). Monosaccharide-containing syrups, after purification, are either fermented or utilized as wood molasses for feeding ruminants. In another approach, xylose, the least soluble component of syrup, is allowed to crystallize. Separated xylose is then hydrogenated over an Ni/Al catalyst at 120°C under 6 x 106 Pa into xylitol. Hemicelluloses, together with proteins, are capable of the Maillard reaction and may contribute to the overall secondary aroma of processed foodstuffs (Tomasik and Zawadzki, 1998). 

As previously mentioned, these reactions are predictable extensions of reactions with monosaccharides. But perhaps the chemistry of oligosaccharides could be a more specific field. How is the reactivity of each hydroxyl group modified by the remainder of the complex sequence, by its configuration, and its conformation Are there functional groups which have lost all reactivity or else, on the contrary, unexpected preferred sites such as the active sites of proteins This area has not yet been explored with really complicated oligosaccharides. 

In the first Section, the dolichol pathway of protein glycosylation is introduced, and the reader is made familiar with the various reactions in the formation of the lipid and carbohydrate moieties of lipid-linked saccharides. Three different classes of compound are known so far (a) isoprenoid alcohol esters of monosaccharide monophosphates, such as D-mannosyl and D-glucosyl (dolichol phosphate), (b) such isoprenoid alcohol esters of saccharide diphosphates as dolichol diphosphate linked to 2-acetamido-2-deoxy-D-glucose and to oligosaccharides, and (c) retinol (D-mannosyl phosphate). The dolichol-linked sugars occur in all eukaryotes. 

Burdon542 has surveyed the current hypotheses for the structure of humic substances and has concluded that the various products from chemical degradations and NMR data are all consistent with their being mixtures of plant and microbial materials and their microbial degradation products. The examination of soil carbohydrates, proteins, lipids, and aromatics supported this view the presence of colour, fluorescence, ESR signals, mellitic acid, and other features do not contradict it. Regarding the Maillard reaction, some free monosaccharides and the necessary amino species are present in soil, so it may proceed, but only to a small extent it is not a major process. However, in marine environments, the relative abundance of carbohydrates and proteins makes them more probable precursors of humic substances than lignin or polyphenols. 

Quantitative precipitin tests were performed as described.73 The amounts of precipitates obtained at the various concentrations were measured by the protein phenol method.74 The inhibition values are recorded in Table I. These inhibition data show that the precipitin reaction between the tetrahet-eropolysaccharide and the anti-GlcA antibodies is strongly inhibited by d-glucuronic acid, but with the exception of galacturonic acid none of the other carbohydrates were inhibitory. The data in the table also show that the carbohydrates tested did not inhibit the precipitin reaction between the polysaccharide and anti-GlcA-Rha antibodies. The monosaccharides alone cannot completely fit the active site of this antibody to give a precipitin test. 

Biotransformation can he viewed as a toolbox to produce polysaccharides with targeted properties [7-10]. One can use hydrolase enzymes to lower the molecular weight. One can use enzymatic reactions to add or modify a substituent on a polysaccharide. One can add a monosaccharide or a second polysaccharide to produce a larger molecule. Some polysaccharides contain proteins or fatty acids, and these can he cleaved or otherwise altered to produce different properties. 

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