Fructose-1,6-bis

Van Schaftingen, E., and Hers, H.-G., 1981. Inhibidon of fructose-1,6-bis-phosphatase by fructose-2,6-bisphosphate. Proceedings of the National Academy of Sciences, USA 78 2861-2863. 

Transfer of the phosphoryl group to ADP in step 10 then generates ATP and gives enolpyruvate, which undergoes tautomerization to pyruvate. The reaction is catalyzed by pyruvate kinase and requires that a molecule of fructose 1,6-bis-phosphate also be present, as well as 2 equivalents of Mg2+. One Mg2+ ion coordinates to ADP, and the other increases the acidity of a water molecule necessary for protonation of the enolate ion. 

Similarly, fructose-6-P, one of the five-sided furan ring sugars we meet in metabolism. [Compound (x)] and fructose,-1,6-bis P [compound (xi)] should be obvious from their structures. 

The interconversion of fructose-6-phosphate and fructose-1,6 bis phosphate is a control point in glycolysis and gluconeogenesis. Gluconeogenesis is a pathway which allows carbon atoms from substrates such as lactate, glycerol and some amino acids to be used for the synthesis of glucose, so it is in effect physiologically the opposite of... 

PFK = phosphofructokinase PK = pyruvate kinase G-6-P = glucose-6-phosphate F-6-P = fructose-6-phosphate F-1,6bisP = fructose-1,6 bis phosphate... 

RAMA rabbit muscle aldolase (fructose-1,6-bis-phosphate aldolase)... 

Changes in allosteric effectors Glucagon lowers the level of fructose 2,6-bisphosphate, resulting in activation of fructose 1,6-bis-phosphatase and inhibition of phosphofructokinase (see Figure... 

A reversible covalent modification that plants use extensively is the reduction of cystine disulfide bridges to sulf-hydryls. Many of the enzymes of photosynthetic carbohydrate synthesis are activated in this way (table 9.3). Some of the enzymes of carbohydrate breakdown are inactivated by the same mechanism. The reductant is a small protein called thioredoxin, which undergoes a complementary oxidation of cysteine residues to cystine (fig. 9.5). Thioredoxin itself is reduced by electron-transfer reactions driven by sunlight, which serves as a signal to switch carbohydrate metabolism from carbohydrate breakdown to synthesis. In one of the regulated enzymes, phosphoribulokinase, one of the freed cysteines probably forms part of the catalytic active site. In nicotinamide-adenine dinucleotide phosphate (NADP)-malate dehydrogenase and fructose-1,6-bis-... 

Enteric bacteria, such as Escherichia coli, assimilate glucose via glycolysis and regulation of the glycolytic pathway is at the site of fructose-1,6-bis-P synthesis (the phosphofructokinase step), and this is the major activator for the E. coli ADPGlc PPase (Preiss, 1984 Preiss and Romeo, 1989,1994). 

For organisms where the predominant pathway is the Entner-Doudoroff pathway, fructose-1,6-bis-P is not a major metabolite in glucose degradation (because glucose-6-P is converted first into 6-P-gluconate and then to 2-keto,3-deoxy,6-P-gluconate) the activators for their ADPGlc PPase are fructose-6-P and pyruvate (Preiss, 1969, 1984 Preiss and Romeo, 1989). 

It was reported by Horecker and coworkers that one class of aldolases (called Class I to distinguish it from the Class II aldolase that is metal ion-dependent) could be inhibited by the addition of borohydride reducing agent to reaction mixtures containing both enzyme and substrate129,130. It was then shown for the fructose- 1,6-bis-phosphate aldolase that the inhibition resulted from reduction of the Schiff base formed between the dihydroxyacetone phosphate substrate and the -amino group of a lysine side chain, thereby compromising the ability of the lysine to participate in subsequent turnover. 

The reaction of the glycolytic enzyme fructose-1,6-bis-phosphate aldolase, perhaps the best-known class I aldolase, is believed to proceed according to the mechanism shown in Scheme 12131. 

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