Polysaccharides lipid intermediates

One of the most impressive findings has been the discovery of lipid intermediates in the biosynthesis of polysaccharides (see Refs. 2 and 465.) At least two structurally different types of these compounds exist the intermediate may be an isoprenoid alcohol ester of the glycosyl pyrophosphate or the analogous derivative of the glycosyl phosphate. Derivatives of the first type are formed by reaction between the sugar nucleotide and the alcohol phosphate, for example, undecaprenyl phosphate (120), which participates in the biosynthesis of Salmonella lipopolysaccharide.466... 

In fungi, and in higher plants, the cell wall is a dynamic structure, changing during growth and differentiation, or in response to environmental factors. The main polysaccharides found in plant cell-walls are listed in this Section. The biosynthesis of those which are synthesized by way of lipid intermediates (see Table V) will be analyzed later. 

The mechanism of synthesis of polysaccharides is a controversial issue. After discovery, by Cardini s group, that starch may be polymerized on a protein,152,153 it was suggested153 that all nascent, polysaccharide chains might be covalently associated with a protein. Connected with the formation of glycoprotein is the involvement of lipid intermediates. We shall analyze the biosynthetic pathways of polysaccharides where partial or complete evidence of this kind of mechanism has been educed. 

The functions of lipid intermediates in the biosynthesis of a man-nan, a bacterial capsular polysaccharide, a cell-wall lipopolysac-charide, and a cell-wall peptidoglycan are respectively discussed in Sections dealing with each (see Sections V,6, p. 396 VI,5,6, and 7, pp. 408, 418, 428). In all these syntheses, the glycosyl groups are... 

The synthesis of SG (and ASG) by cell-free particulate fractions from plants has been reported by many researchers (e.g., Hou et al., 1%7, 1%8 Eichenberger and Newman, 1%8 Kauss, 1968 Ongun and Mudd, 1970 La-vintman and Cardini, 1970). In many cases the research interest was in polysaccharide biosynthesis and the possible involvement of lipid intermediates. There is no evidence that glycosylated sterols participate in the synthesis of polysaccharides. 

The biosynthesis of poly-2 -> 8 or -2 9-(A-acetyl-D-neuraminic acid) capsular polysaccharide (colominic acid) from E. coli or N. meningitidis (see Chapter 6, Fig. 6.20 for the structures) has also been shown to involve a polyprenol phos-phoryl A-acetyl-D-neuraminic acid lipid intermediate formed from CMP-NeuNAc [67,68]. This is an example of the biosynthesis of a homopolysaccharide that requires a polyprenol phosphate coenzyme lipid carrier. 

Stipe powder of C. comatus (100 g) was extracted three times with 1 L 95% ethanol under reflux for 2 h to remove lipid, and the residue was extracted three times with 2 L distilled water for 2 h at 80 °C with intermediate centrifugation (2000 x g, 15 min). After concentrating the collected aqueous supernatants to 400 mL (reduced pressure at 40 °C), a precipitation was performed with 3 volumes of 95% ethanol. The precipitate was washed with ethanol and acetone, and then dried at 40 C, yielding crude polysaccharide material. Crude polysaccharide material was dissolved in 100 mL 0.2 M sodium phosphate buffer (pH 6.0), and after centrifugation the solution was applied to a DEAE-Sepharose CL-6B column. 

In addition to its role as an intermediate in cholesterol biosynthesis, isopentenyl pyrophosphate is the activated precursor of a huge array of biomolecules with diverse biological roles (Fig. 21-48). They include vitamins A, E, and K plant pigments such as carotene and the phytol chain of chlorophyll natural rubber many essential oils (such as the fragrant principles of lemon oil, eucalyptus, and musk) insect juvenile hormone, which controls metamorphosis dolichols, which serve as lipid-soluble carriers in complex polysaccharide synthesis and ubiquinone and plastoquinone, electron carriers in mitochondria and chloroplasts. Collectively, these molecules are called isoprenoids. More than... 

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