A-D-Fructose 6-phosphate

Step 2 is the isomerization of a-D-glucose 6-phosphate, by glucose-6-phosphate isomerase, to a-D-fructose 6-phosphate. This is a freely reversible reaction. 

Step 3 is the phosphorylation of a-D-fructose 6-phosphate to a-D-fructose 1,6-bisphosphate. The enzyme is phosphofructokinase and ATP and Mg2+ are required. 

Leloir and Cardini (177a) found later that wheat germ contains another enzyme which will form sucrose phosphate when a-D-fructose 6-phosphate... 

Schurmann, M., Schurmann, M. and Sprenger, G.A. (2002) Fructose 6-phosphate aldolase and 1-deoxy-D-xy lulose 5-phosphate synthase from Escherichia coli as tools in enzymatic synthesis of 1-deoxysugars. Journal of Molecular Catalysis B, Enzymatic, 19, 247-252. 

It has recently been reported21 that a mixed osazone of 3,4-di-O-methyl-D-glucose can be converted, by treatment with p-nitrobenzaldehyde, into an osone which reacts with phenylhydrazine to give 3,4-di-O-methyl-D-glucose phenylosazone. Von Lebedev29 claimed to have obtained D-glu-cosone 6-phosphate, isolated as an amorphous lead salt, by the action of hydrochloric acid on the phenylosazone prepared from D-fructose 6-phosphate. 

Lohmann118 detected an enzyme in muscle extracts, found later in plants and yeasts,104Co) 117,118 termed phosphoglucoisomerase, (optimum pH 9), which catalyzes the interconversion of D-glucose 6-phosphate (XVI) and D-fructose 6-phosphate (XVII). At equilibrium, which is attained rapidly, there is about 70 % of the former and 30 % of the latter. In a similar conver-... 

Fructose 1,6-diphosphatase hydrolyzes D-fructose 1,6-diphosphate to give D-fructose 6-phosphate and PO . It is a key enzyme in the gluconeo-genesis pathway. Two divalent metal ions (Mg2+, Mn2+, Zn2+, and Co2+) are involved in catalysis. In the enzyme isolated from pork kidney the metal-metal distance accounts to 3.7 A [12]. A reaction mechanism similar to that of protein phosphatase 1 was proposed, but leaving group stabilization by metal coordination of the ester oxygen atom appears to be absent (Figure 6) [12]. 

Transaldolase, which catalyzes reactions with d-erythrose 4-phosphate and D-fructose 6-phosphate as substrates. As in the case of fructose-1,6-bisphosphate aldolase, this enzyme uses a e-amino side-chain to form a Schiff base intermediate. In this case, however, the triose phosphate moiety is not released but is transferred to the other aldose (in this case, the aldotetrose). 

It had been known from at least the time of Pasteur that the presence of sodium or potassium phosphate aided the progress of a yeast fermentation. Later intensive study showed that a complex group of enzymes (phosphatases and phosphorylases) was responsible for the phosphorylation, dephosphorylation and interconversion of D-glucose 6-phosphate, D-fructose 6-phosphate, D-fructose 1,6-diphosphate and similar substances in various types of cells and muscle tissue. Detailed reviews of the field are available. - A further advance was made in 1936, when Cori and Cori noted that in certain circumstances well-washed frog muscle immersed in a sodium phosphate buffer utilized the inorganic phosphate to produce a new hexose phosphate (the Cori ester). This compound was later shown to be a-D-glucopyranose-l-phosphate and yielded crystalline dipotassium and brucine salts. The Cori ester arose because... 

The long-known stimulating effect of mono- and polynitro com-pounds on the onset of fermentation in yeast maceration juice has been reinvestigated by Vandendriessche. The induction time is shortened significantly by 2,4- or 2,5-dinitrophenol, while 2,6-dinitro-phenol did not show such an effect. The influence is evident when using as substrates the fermentable hexoses and D-fructose-6-phosphate, but not hexose diphosphate. According to MarkoviCev a stimulation of the oxidation processes can be proved thereby. It is probable that these effects are related to the known phytochemical reduction of nitro compounds (see pp. 98 and 99). 

A valuable series of comparative experiments was performed by Schwim-mer and Olcott151 on the reaction of glycine with D-glucose, D-fructose, D-glucose 6-phosphate, D-fructose 6-phosphate, and D-fructose 1,6-diphosphate in the presence and absence of a phosphate buffer at pH 6.5. The rate of browning at 70° (over 18 hours) was determined colorimetrically at 420 mp. An increase in the rate of browning was observed for the hexose 6-phosphates, as compared with the unsubstituted sugars. Similarly, the... 

In a very imaginative piece of research Frost and coworkers have developed a plasmid-based method for synthesizing aromatic amino acids, by incorporating the genes that code for the enzymes that perform the series of conversions from D-fructose-6-phosphate to D-erythrose-4-phosphate to 3-deoxy-D-arabinoheptulosonic acid-7-phos-phate (DAHP) near each other on a plasmid that can be transformed in E. coli. The enzymes are the thiamin diphosphate-dependent enzyme transketolase in the nonoxida-tive pentose shunt and DAHP synthase. The DAHP is then converted to the cyclic dehydroquinate, a precursor to all aromatic amino acids L-Tyr, L-Phe and L-Trp165,166 (equation 27). 

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