This reference may be of help to you.

https://www.researchgate.net/publication/229115012_A_microplate_assay_for_D-xyloseD-glucose_isomerase

Article A microplate assay for D-xylose/D-glucose isomerase

Dear Robson,

Herein the protocol taken from a publication entitled "Directed Evolution of Xylose Isomerase for Improved Xylose Catabolism and Fermentation in the Yeast Saccharomyces cerevisiae " Appl. Environ. Microbiol. August 2012 vol. 78 no. 16 5708-5716.

In vitro xylose isomerase activity measurements.Xylose isomerase activities from cell extracts were assayed by measuring the decrease of NADH in 1 ml of reaction mixture at 340 nm using a spectrophotometer (18). The reaction mixture contained 100 mM Tris-HCl buffer (pH 7.5), 0.15 mM NADH, 10 mM MgCl2, and 2 U sorbitol dehydrogenase (Roche, Mannheim, Germany). The cell extracts were prepared from yeast transformants cultivated until the early exponential growth phase in selective medium by using YPER Plus Dialyzable Yeast Protein Extraction Reagent (Thermo Scientific, Rockford, IL) The protein contents of the cell extracts were determined by a Bradford assay using a Pierce BCA Protein Assay Kit (Thermo Scientific, Rockford, IL). Enzyme assays were performed in biological triplicate, and 25 to 500 mM xylose was used to determine kinetic parameters.

http://aem.asm.org/content/78/16/5708.full

https://microbialcellfactories.biomedcentral.com/articles/10.1186/s12934-015-0253-1

For microplates, see the following:

A modification of the resorcinol method of Kulka1 for the determination of ketoses is described. Though being a stopped enzyme test, it is much more sensitive than the carbazol method and by applying microtiter plates and measuring with an ELISA reader, a large number of tests can be performed within a short time, thereby facilitating initial velocity studies.The test is linear up to a concentration of 2.5 mmd-xylulose even in the presence of 10 mmd-xylose and 2 mmd-fructose in the presence of 10 mmd-glucose. The sensitivity is 25 μm for xylulose and 38 μm for fructose. The test method is insensitive to perturbations of substances frequently used in isolation procedures such as ammonium sulfate, Triton X-100, PEG 6000, sodium dodecyl sulfate, and ethanol in moderate concentrations.

https://www.researchgate.net/publication/229115012_A_microplate_assay_for_D-xyloseD-glucose_isomerase

Yeast's intracelular crude extract can be measured using the above mentioned protocol.

For more details on this topic, please use the three links indicated above text.

Hoping this will be helpful,

Rafik

Article A microplate assay for D-xylose/D-glucose isomerase

Thank you so much Rafik. That's exactly what I needed.

kindest regards,

Robson