Carbohydrates, xviii

Table XVIII contains the 13C-n.m.r.-spectral data for the model compounds a,/ -Araf — Hyp and a,/ -Ara/— Hyp. The assignments of Qfi and Cs of Hyp were readily obtained19 by comparison with 13C data for L-Hyp in the free amino acid form and for L-Hyp residues of peptides.109 The chemical shift of C 5 was, as expected, 7-8 p.p.m. downfield from the values reported for nonglycosylated L-Hyp. The chemical shifts of C and Cy appeared in the same region as carbohydrate resonances and were therefore identified through their chemical shift-pH dependence.19 The chemical shift of the / -anomeric carbon atom in compound 60 is rather up-field, in agreement with a syn orientation for the C-1 - O-1 and...

Roos, Y., Karel, M. Thermal history and properties of frozen carbohydrate solutions. Paper 350. International Institute of Refrigeration < IIR> (XVIII h Congress, Montreal 1991)... 

Studies on Uronic Acid Materials. Part XVIII. Light-scattering Studies on Some Molecular Weight Fractions from Acacia Senegal Gum, D. M. W. Anderson, Sir Edmund Hirst, S, Rahman, and G. Stainsby, Carbohydr. Res., 3, 308 (1967). 

The various types of carbohydrates considered in this chapter are shown in formulas I-XVIII. The two ring forms (II and III) of the aldoses are shown because careful oxidation can produce the lactones X and XI directly without breaking the oxygen bridge. In most cases, however, the products of oxidation have been isolated as salts of aldonic acids (IX) thus the nature of the initial oxidation product, either a lactone having the same ring structure as the sugar, or possibly the free... 

The breakdown of activated acetate itself takes place in the citric acid cycle (Krebs cycle tricarboxylic acid cycle). In this cycle the pathways of protein, fat, and carbohydrate catabolism are united. Furthermore, the cycle provides many of the necessary components for the synthesis of endogenous substances. The citric acid cycle therefore encompasses a large pool of common intermediates, which can be used either for synthesis of new cell material or for degradation to gain energy. The full significance of these interrelationships will be demonstrated later (cf. Chapt. XVIII). 

The cleavage products follow separate pathways of metabolism. Glycerol, closely related to carbohydrates, is either utilized for the biosynthesis of fructose and glucose or, after phosphorylation, is broken down in the same way as the carbohydrates (Chapt. XVIII-1). Fatty acids are decomposed according to the rules of /3-oxidation to C2 units (activated acetate) which may then either be used for biosynthesis or be oxidized to CO2 and H2O through the citrate cycle (Chapt. XI) and the respiratory chain. 

The preceding paragraphs undoubtedly have revealed the complicated and diverse nature of carbohydrate metabolism, both on the level of interconversions among the carbohydrates and on that of degradative reactions for the production of energy. Part of the energy is derived anaerobically by substrate-linked phosphorylation the major part, however, is liberated in the respiratory chain. The situation is further complicated by the obvious fact that carbohydrate metabolism is not an isolated system of reactions, but is closely tied to other pathways and reaction cycles through common intermediates. A separate chapter (Chapt. XVIII) is devoted to such interrelationships. 

Heat of Combustion. Carbohydrates, fats, and proteins can replace each other as nutrients to a large extent. This is not very surprising in view of our discussion of metabolism (Chapt. XVIII), in which the concept of a common terminal metabolic pathway (Netter) through the citrate cycle and the respiratory chain was developed. 

J.A. Wright and N.F. Taylor, Fluorinated carbohydrates. Part XVIII. 9-(3-Deo3 -3-fluoro-j8-D-jQflofuranosyl)adenine and 9-(3-Deo)g -3-fluoro-a-D- grIofurano l)adenine Carbohydr. Res. 6 347 (1968). 

G. Hodosi and P. Kovac, XVIII Int Carbohydr. Symposium Abstr., Milano, 1996, pp. 394. 

D. Garozzo, G. Impallomeni, E. Spina, L. Sturiale, XVIII Int. Carbohydr. Symp., 1996, Milan, Italy, AO0I7. 

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