Embden ester

The magnesium and zinc salts also are sol in water The equilibrium mixture of 75-80% glucose-6-phosphate and 20-25% fructose-6-phosphate is called lactacidogea Or Embden ester. 

Embden ester a mixture of D-glueose-6-phos-phate and D- uetose 6-phosphate, both of which are intermediates in glycolysis. 

Metabolic Functions. The formation of phosphate esters is the essential initial process in carbohydrate metaboHsm (see Carbohydrates). The glycolytic, ie, anaerobic or Embden-Meyerhof pathway comprises a series of nine such esters. The phosphogluconate pathway, starting with glucose, comprises a succession of 12 phosphate esters. 

Yeast (qv) metabolize maltose and glucose sugars via the Embden-Meyerhof pathway to pymvate, and via acetaldehyde to ethanol. AH distiUers yeast strains can be expected to produce 6% (v/v) ethanol from a mash containing 11% (w/v) starch. Ethanol concentration up to 18% can be tolerated by some yeasts. Secondary products (congeners) arise during fermentation and are retained in the distiUation of whiskey. These include aldehydes, esters, and higher alcohols (fusel oHs). NaturaHy occurring lactic acid bacteria may simultaneously ferment within the mash and contribute to the whiskey flavor profile. 

The three major processes in carbohydrate metabolism, namely the Calvin cycle of photosynthesis (Figure 11.19), the Embden-Meyerhof scheme of glycolysis (Figure 11.20) and the Krebs cycle of respiration (Figure 11.21) all require ATP and/or other phosphate esters such as NAD+, NADP or Acetyl-CoA to act as energy carriers. Both ATP and NADPH are involved in the fixation of nitrogen and numerous other biochemical cycles (Section 11.5). 

The Embden-Meyerhof pathway with the Krebs tricarboxylic acid cycle is the most universal glucose oxidation system found in nature. It is, however, by no means the only one. Many variations of the Krebs cycle are known to exist in different organisms and species, although phosphate esters are involved in all of these at some stage or other. 

An important discovery, that of free adenylic acid in muscle, was made by Embden in 1927. Muscle adenylate was recognized as the 5 -mono-phosphoric ester of adenosine because enzymatic deamination yielded the known inosinic acid. It was shown at that time that the deaminase preparations from muscle did not deaminate the adenylic acid isolated from alkaline hydrolysates of yeast nucleic acid as well, differences were apparent in the chemical properties of the adenylic acids from these two sources. Yeast adenylic acid and the other nucleotides from alkaline hydrolysates of RNA were ultimately shown to be mixtures of the 2 - and 3 -phospho esters. In 1929 the isolation of adenosine triphosphate from muscle was reported by Lohmann and independently by Fiske and Subbarow. The discovery of adenosine diphosphate followed in 1935. 

Glucose Monophosphates.—A crude monophosphate (Robison s ester) has been obtained by the action of yeast juice on glucose or fructose. It is a mixture of fructose monophosphate (Neuberg s ester) and glucopyranose-6-phosphoric acid (Embden s ester). The two esters have been separated by fractional crystallisation of their brucine salts. A glucopyranose-1-monophosphate (Cori s ester) is obtained by the action of phosphate on minced muscle. 

Two phosphate esters, fructose 6-phosphate and fructose 1,6-diphosphate (the Harden-Young ester) are biochemically significant because they are intermediates in the breakdown of glucose according to the Embden-Meyerhof pathway (Section 7) this pathway is actually the route of breakdown of fructose 1,6-diphosphate. 

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