Carbohydrate-enzyme complexes

The stability of a phenylesterase in soil was considered to be the result of a carbohydrate-enzyme complex, although in this instance, the existence of a carbohydrate-protein bond through N-acetylhexosamine-tyrosine is postulated. Hyaluronidase treatment increases the activity of the enzyme. 

Thiamin has a central role in energy-yielding metabo-hsm, and especially the metabohsm of carbohydrate (Figure 45-9). Thiamin diphosphate is the coenzyme for three multi-enzyme complexes that catalyze oxidative decarboxylation reactions pymvate dehydrogenase in carbohydrate metabolism a-ketoglutarate dehydro-... 

Fixation of carbon dioxide by biotin-enzyme complexes is not unique to acetyl-CoA, and another important example occurs in the generation of oxaloacetate from pyravate in the synthesis of glucose from non-carbohydrate sources (gluconeogene-sis). This reaction also allows replenishment of Krebs... 

Chapters 17 through 21 deal with carbohydrate-enzyme systems. Hehre presents some new ideas on the action of amylases. Kabat presents some new immunochemical studies on the carbohydrate moiety of certain water-soluble blood-group substances and their precursor antigens. Hassid reviews the role of sugar phosphates in the biosynthesis of complex saccharides. Pazur and co-workers present information obtained by isotopic techniques on the nature of enzyme-substrate complexes in the hydrolysis of polysaccharides. Gabriel presents a common mechanism for the production of 6-deoxyhexoses. An intermediate nucleoside-5 -(6-deoxyhexose-4-ulose pyrophosphate) is formed in each of the syntheses. 

Claisen reactions involving acetyl-CoA are made even more favourable by first converting acetyl-CoA into malonyl-CoA by a carboxylation reaction with CO2 using ATP and the coenzyme biotin (Figure 2.9). ATP and CO2 (as bicarbonate, HC03-) form the mixed anhydride, which car-boxy lates the coenzyme in a biotin-enzyme complex. Fixation of carbon dioxide by biotin-enzyme complexes is not unique to acetyl-CoA, and another important example occurs in the generation of oxaloacetate from pyruvate in the synthesis of glucose from non-carbohydrate sources... 

The majority of the industrially applied biotechnical processes for the generation of flavour preparations relies on reactions with isolated enzymes and enzyme complexes. The basic principle of enzymatic reactions is mostly hydrolytic decomposition or transformation of the most important biological substance categories like proteins, carbohydrates, lipids and acids. 

The second metabolic pathway which we have chosen to describe is the tricarboxylic acid cycle, often referred to as the Krebs cycle. This represents the biochemical hub of intermediary metabolism, not only in the oxidative catabolism of carbohydrates, lipids, and amino acids in aerobic eukaryotes and prokaryotes, but also as a source of numerous biosynthetic precursors. Pyruvate, formed in the cytosol by glycolysis, is transported into the matrix of the mitochondria where it is converted to acetyl CoA by the multi-enzyme complex, pyruvate dehydrogenase. Acetyl CoA is also produced by the mitochondrial S-oxidation of fatty acids and by the oxidative metabolism of a number of amino acids. The first reaction of the cycle (Figure 5.12) involves the condensation of acetyl Co and oxaloacetate to form citrate (1), a Claisen ester condensation. Citrate is then converted to the more easily oxidised secondary alcohol, isocitrate (2), by the iron-sulfur centre of the enzyme aconitase (described in Chapter 13). This reaction involves successive dehydration of citrate, producing enzyme-bound cis-aconitate, followed by rehydration, to give isocitrate. In this reaction, the enzyme distinguishes between the two external carboxyl groups... 

Bacteria also secrete both endo- and exoenzymes, some of which form complexes that act jointly in degrading cellulose to form the carbohydrate nutrients which the microorganisms need for survival [12, 13]. Both the enzyme complexes, which generally contain from two to four different enzymes, and the individual enzymes can attack cellulose either from a dissolved state in aqueous solution or from a state in which the enzyme is bound to the outer cell wall of the bacteria. In most cases, the principal product is cellobiose. In contrast, while multiple enzymes may be involved, enzyme complexes are seldom found with fungi. 

A. Pasternak, W.Q. Yao, P.A. Sprengeler, M.K. Holloway, L.C. Kuo, Z.G. Chen, P.L. Darke, W.A. Schleif, An orally bioavailable pyrrolinone inhibitor of Hiv-1 protease computational analysis and X-ray crystal structure of the enzyme complex, J. Med. Chem. 1997, 40, 2440-2444 P.V. Murphy, J.L. O Brien, L.J. Gorey-Feret, A.B. Smith, Synthesis of novel Hiv-1 protease inhibitors based on carbohydrate scaffolds, Tetrahedron 2003, 59, 2259-2271 P.V. Murphy, J.L. O Brien, L.J. Gorey-Feret, A.B. Smith, Structure-based design and synthesis of Hiv-1 protease inhibitors employing beta-D-mannopyranoside scaffolds, Bioorg. Med. Chem. Lett. 2002, 12, 1763-1766. 

In a well-fed individual, the quantity of the fatty acid synthase complex is increased (see Fig. 36.4). The genes that produce this enzyme complex are induced by increases in the insulin/glucagon ratio. The amount of the complex increases slowly after a few days of a high-carbohydrate diet. 

This enzyme complex constitutes a point of no return for carbon atoms derived from glucose in humans and most other higher organisms there is no pathway that enables the synthesis of carbohydrate from the... 

The pheromone-biosynthesis of most female butterflies starts de novo from acetate, which originates from the carbohydrate metabolism, on a multi-enzyme complex along the general pathway for the biosynthesis of fatty acids. 

HPLC and GC have been the techniques of choice for analyzing oligosaccharides. These techniques have worked well for small oUgosaccharides or purified preparations. However, these techniques have not been successful for the analysis of oUgosaccharides in complex foods. Here, the carbohydrates in complex foods have been initially hydrolyzed using enzymes to See the monosaccharides followed by their detemiination using HPLC. For example, the malto-oligosaccharides have to be extracted before their analysis of starch. Otherwise, they are recovered as starch. 

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