Phosphohexose isomerase

Enzymes, measured in clinical laboratories, for which kits are available include y-glutamyl transferase (GGT), alanine transferase [9000-86-6] (ALT), aldolase, a-amylase [9000-90-2] aspartate aminotransferase [9000-97-9], creatine kinase and its isoenzymes, galactose-l-phosphate uridyl transferase, Hpase, malate dehydrogenase [9001 -64-3], 5 -nucleotidase, phosphohexose isomerase, and pymvate kinase [9001-59-6]. One example is the measurement of aspartate aminotransferase, where the reaction is followed by monitoring the loss of NADH ... 

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. 

C7. Chaput, M., Claes, V., Portetelle, D., Cludts, L, Cravador, A., Burny, A., Gras, H and Tartar, A., The neurotrophic factor neuroleukin is 90% homologous with phosphohexose isomerase. Nature 332,454-455 (1988). 

Schwartz, M. K., and Bodansky, 0., Use of commercially available preparations of fructose-6-phosphate in the determination of phosphohexose isomerase activity. Anal. Biochem. 11, 48-53 (1965). 

FIGURE 9 Isomerization and elimination reactions (a) The conversion of glucose 6-phosphate to fructose 6-phosphate, a reaction of sugar metabolism catalyzed by phosphohexose isomerase. (b) This reaction proceeds through an enediol intermediate. The curved blue ar-... 

Conversion of Glucose 6-Phosphate to Fructose 6-Phosphate The enzyme phosphohexose isomerase (phospho-glucose isomerase) catalyzes the reversible isomerization of glucose 6-phosphate, an aldose, to fructose 6-phosphate, a ketose ... 

The reaction mechanism is similar to the reaction promoted by phosphohexose isomerase in step (2) of glycolysis (Fig. 14-4). After the triose phosphate isomerase reaction, C-1, C-2, and C-3 of the starting glucose are chemically indistinguishable from C-6, C-5, and C-4, respectively (Fig. 14-6), setting up the efficient metabolism of the entire six-carbon glucose molecule. 

When real data from the experiment on glycolysis in a rat liver extract (Fig. 15-33) were subjected to this kind of analysis, investigators found flux control coefficients (for enzymes at the concentrations found in the extract) of 0.79 for hexoldnase, 0.21 for PFK-1, and 0.0 for phosphohexose isomerase. It is not just fortuitous that these values add up to 1.0 we can show that for any complete pathway, the sum of the flux control coefficients must equal unity. 

The chloroplast stroma contains all the enzymes necessary to convert the triose phosphates produced by C02 assimilation (glyceraldehyde 3-phosphate and dihydroxyacetone phosphate) to starch, which is temporarily stored in the chloroplast as insoluble granules. Aldolase condenses the trioses to fructose 1,6-bisphos-phate fructose 1,6-bisphosphatase produces fructose 6-phosphate phosphohexose isomerase yields glucose 6-phosphate and phosphoglucomutase produces glucose 1-phosphate, the starting material for starch synthesis (see Section 20.3). 

Adds coverage of the mechanisms of phosphohexose isomerase and aldolase... 

In the presence of excess phosphohexose isomerase and glucose-6-phos-phate dehydrogenase the rate of reduction of TPN is proportional to the rate of cleavage of fructose diphosphate. For cases when small, quantities of fructose diphosphate must be used, a second spectrophoto-metric assay, in which fructose diphosphate is regenerated, has been proposed 20). Fructose 6-phosphate is phosphorylated with ATP and phosphofructokinase, and the adenosine diphosphate (ADP) produced is measured with phosphoenolpyruvate and lactic dehydrogenase ... 

Glucose-6-phosphate. Fructose-6-phosphate Phosphohexose isomerase +0.4 -.60... 

In addition to serving as structural motifs, enols and enolates are involved in diverse biological processes. Several enol/enolate intermediates have been proposed to be involved in glycolysis (Section IV.A), wherein c/ -enediol 21 is proposed to be an intermediate in the catalytic mechanism of phosphohexose isomerase and an enol-containing enamine intermediate (22) has been proposed in the catalytic pathway of class I aldolase. In the case of glucose-fructose (aldose-ketose) isomerization, removal of the proton on Cl-OH produces the aldose while deprotonation of C2-OH yields the ketose, which is accompanied by protonation at the C2 and Cl positions, respectively. There are several cofactors that are involved in various biological reactions, such as NAD(H)/NADP(H) in redox reaction and coenzyme A in group transfer reactions. Pyridoxal phosphate (PLP, 23) is a widely distributed enzyme cofactor involved in the formation of a-keto acids, L/D-amino... 

B22. Bodansky, O., Serum phosphohexose isomerase in cancer. III. As an index of tumor growth in metastatic carcinoma of the prostate. Cancer 8, 1087-1114 (1955). 

Phosphoglucose isomerase. Phosphohexose isomerase. Phosphohexomutase. Oxoisomerase. 

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