Glucose-phosphate isomerase

PHOSPHOGLUCOSE ISOMERASE Glucose-6-phosphate isomerase, PHOSPHOGLUCOISOMERASE D-Glucose 6-phosphate synthesis, 6-PHOSPHO-/3-GLUCOSIDASE GLUCOSE-1-PHOSPHATE URIDYLYLTRANS-FERASE... 

Glucose-6-phosphate isomerase efficiency of 692 turnover number of 692... 

Glucose 6-phosphate isomerase 279 Glucosidases—see lysozyme Glutamate dehydrogenase 167 Glutamine synthetase 298 Glyceraldehyde 3-phosphate... 

These three biochemical reactions are catalyzed by hexokinase (EC 2.7.1.1), glucose-6-phosphate isomerase (EC 5.3.1.9), and 6-phosphofructokinase (EC 2.7.1.11), respectively. The EC numbers are from Enzyme Nomenclature (Webb, 1992). The first step is to write the conservation matrix for this reaction system at specified pH because that will show how to calculate the further transformed Gibbs energies of formation at specified [ATP] and [ADP]. 

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. 

Stevens and Stevens (1979) measured the hydration dependence of glucose-6-phosphate dehydrogenase, hexokinase, fumarate hydratase (fumarase), and glucose-6-phosphate isomerase (phosphoglucose isom-erase) over the range 0.1-0.6 h. Serum albumin was used as a carrier protein to buffer the water content. The hydration isotherms of the enzymes and the serum albumin were assumed to be similar. For the first three enzymes activity was detected (0.05% of full solution activity) near 0.2 h. Activity was measurable for the isomerase at 0.15 h. In all cases, even at 0.3 h, the activity in the powder was less than 5% of the solution rate. Diffusion of substrates in the powder may be rate limiting. The amount of albumin in the powder affected the rate. 

Phosphorylation and isomerization. Glucose, produced by the digestion of dietary carbohydrate., is first phosphorylated at the hydroxyl group on C6 by reaction with ATP in a process catalyzed by the enzyme hexokinase. The glucose 6-phosphate that results is isomerized by glucose 6-phosphate isomerase to fructose 6-phosphate. As the open-chain structures in Figure 29.4 show, this isomerization reaction takes place by keto-enol tautomerism (Section 22.1), since both glucose and fructose share a common enol ... 

---