Glucose-6-phosphate isomerase assay

Figure 3(A). Comparison of temperature optima for activities of glucose isomerase, amylase, and >galactosidase. Enzymes were assayed with cell extract from xylose-grown cells. A 100% activity value corresponds to 0.60, 0.58, and 0.46 U/mg for glucose isomerase, amylase, and -galactosidase, respectively. Cell extracts in 50 mM sodium phosphate buffer (pH 7.0), 100 mM sodium acetate buffer (pH 5.5), and 100 mM sodium phosphate buffer (pH 6.0) for glucose isomerase, amylase, and -galactosidase, respectively, were preincubatcd at the indicated temperatures, prior to the assay for residual enzyme activities. Reprinted with permission from ref. 20. Copyright 1990 American Society for Microbiology.

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 ... 

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