Sugars glycolysis

While this alkalinity is eventually neutralised by organic acid synthesis from sugar (glycolysis plus PEP carboxylase - ref. 4), the immediate effect is that two microequivalents of hydroxyl ions are produced in the chloroplast stroma for each microequivalent of nitrite or sulphate photoreduced via ferredoxin. The observed maximum rates of nitrate assimilation in leaves are about 5 microequivalents per mg chlorophyll per hour, producing 10 microequivalents of hydroxyl ions in the chloroplast stroma. 

In contrast with the well-known Embden-Meyerhof-Pamass glycolysis pathway for the conversion of hexose sugars to alcohol, the steps in conversion of ethanol to acetic acid remain in some doubt. Likely, ethanol is first oxidized to acetaldehyde and water (39). For further oxidation, two alternative routes are proposed more likely, hydration of the acetaldehyde gives CH2CH(OH)2, which is oxidized to acetic acid. An alternative is the Cannizzaro-type disproportionation of two molecules of acetaldehyde to one molecule of ethanol and one molecule of acetic acid. Jicetobacter... 

The glycolytic pathway described in this chapter begins with the breakdown of glucose, but other sugars, both simple and complex, can enter the cycle if they can be converted by appropriate enzymes to one of the intermediates of glycolysis. Figure 19.32 shows the mechanisms by which several simple metabolites can enter the glycolytic pathway. Fructose, for example, which is pro-... 

Another simple sugar that enters glycolysis at the same point as fructose is mannose, which occurs in many glycoproteins, glycolipids, and polysaccharides (Chapter 7). Mannose is also phosphorylated from ATP by hexokinase, and the mannose-6-phosphate thus produced is converted to fructose-6-phosphate by phosphomannoisomerase. 

A somewhat more complicated route into glycolysis is followed by galactose, another simple hexose sugar. The process, called the Leloir pathway after Luis Leloir, its discoverer, begins with phosphorylation from ATP at the C-1 position by galactokinase ... 

Figure 10.18 Enzymatic in situ generation of dihydroxyacetone phosphate from fructose 1,6-bisphosphate (b), with extension to an in vitro artificial metabolism for its preparation from inexpensive sugars alongthe glycolysis cascade (a), and utilization for subsequent stereoselective carbon-carbon bond formation using an aldolase with distinct stereoselectivity (c).

F g- 3-3 The biochemical pathway of glycolysis, which obtains energy from the breakdown of 6-carbon sugars to a pair of 3-carbon pyruvate molecules. Enzymes at each reaction in the sequence are in italics. The energy generated is stored in the form of ATP (see Fig. 3-2). 

Derivatives of trioses, tetroses, and pentoses and of a seven-carbon sugar (sedohepmlose) are formed as meta-bohc intermediates in glycolysis and the pentose phosphate pathway. Pentoses are important in nucleotides. 

The role of L-glycerose as a precursor of l sugars is doubtful, since it inhibits glycolysis in plants and animals, probably by the formation of L-sorbose 1-phosphate, which inhibits hexokinase.74-75... 

Of course, it is now established that the glycolysis of glucose to carbon dioxide and ethanol occurs by way of a complex pathway involving 10 different enzymes acting on a variety of sugar phosphate intermediates. The extracellular enzyme preparation that Fischer used was termed invertin, the origin of the term for the enzyme we now know as invertase. He termed the intracellular enzyme yeast-glucase (31) and this enzyme is of the type we now refer to as an amylase. 

ATP-proton motive force interconversion Electron transport Entner-Doudoroff Fermentation Glycolysis/gluconeogenesis Pentose phosphate pathway Pyruvate dehydrogenase Sugars TCA cycle Methanogenesis Polysaccharides Other... 

We now turn to the metabolic fate of these sugars, fit most cells, the metabolic pathway responsible is termed glycolysis or the glycolytic pathway. The starting point for glycolysis is D-glucose. The end products of glycolysis... 

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