Fructose 6-phosphate metabolism

Fructose can be metabolized by two routes. In adipose tissue and muscle, hexokinase can phosphorylate fructose to fructose 6-phosphate that then enters glycolysis. In liver, most of the enzyme present is glucokinase not hexokinase and this does not phosphorylate fructose. In this tissue, fructose is metabolized instead by the fructose 1-phosphate pathway. 

Fructose is metabolized mainly in the liver, where it is converted to fructose 1-phosphate and cleaved to produce dihydroxyacetone phosphate and glyceraldehyde, which may be phosphorylated to glyceraldehyde 3-phosphate. These two triose phosphates are intermediates of glycolysis. 

The conversion of fructose-1-phosphate into glycolytic intermediates bypasses two regulatory steps (the reactions catalyzed by hexokinase and PFK-1) thus fructose is metabolized more quickly than glucose. 

Fructose-l-phosphate Metabolism. A kinase in mammalian liver has been found to phosphorylate fructose on carbon l. This is in contrast to... 

Fructose is metabolized by both fructose hexokinase and PTS (Tonouchi et al. 1996). Fructose is phosphorylated to F6P by hexokinase or to fructose-1-phosphate (FIP) via PTS. F6P is then converted by phosphoglucomutase to G6P, which can subsequently be used for cellulose synthesis or metabolized through the... 

Reactions 1 to 7 take place in the liver and form the major route by which dietary fructose is metabolized other, minor, reactions take place in other tissues. Reaction 1 is catalysed by fructose kinase (EC 2.7.1.4) and reaction 2 by fructose-1-phosphate aldolase. 

Phosphate esters of glucose, fructose, and other monosaccharides are important metabolic intermediates, and the ribose moiety of nucleotides such as ATP and GTP is phosphorylated at the 5 -position (Figure 7.13). 

One of the steps in the biological pathway for carbohydrate metabolism is the conversion of fructose 1,6-bisphosphate into dihydroxyacetone phosphate and glyceraldehyde 3-phosphate. Propose a mechanism for the transformation. 

The most convenient method is the formation of two equivalents of (25) by retro-aldol cleavage from commercially available (26) by the combined action of FruA and triose phosphate isomerase (Figure 10.18 inset) [84]. This scheme has been extended into a highly integrated, artificial metabolism for the efficacious in situ preparation of (25) from inexpensive feedstock such as glucose and fructose (two equivalents of... 

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).

Glucose 6-phosphate is an important compound at the junction of several metabolic pathways (glycolysis, gluconeogenesis, the pentose phosphate pathway, glycogenosis, and glycogenolysis). In glycolysis, it is converted to fructose 6-phosphate by phosphohexose-isomerase, which involves an aldose-ketose isomerization. 

The pentose phosphate pathway is an alternative route for the metabolism of glucose. It does not generate ATP but has two major functions (1) The formation of NADPH for synthesis of fatty acids and steroids and (2) the synthesis of ribose for nucleotide and nucleic acid formation. Glucose, fructose, and galactose are the main hexoses absorbed from the gastrointestinal tract, derived principally from dietary starch, sucrose, and lactose, respectively. Fructose and galactose are converted to glucose, mainly in the liver. 

Glucose phosphate isomerase (GPI) catalyzes the reversible interconversion of glucose-6-phosphate and fructose-6-phosphate. GPI plays an essential role in carbohydrate metabolism in all cells of the body. The substrates of this enzyme, ffuc-... 

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