A MICROPLATE ASSAY FOR D-XYLOSE D-GLUCOSE ISOMERASE/

A modification of the resorcinol method of Kulka(1) for the determinat ion of ketoses is described. Though being a stopped enzyme test, it is much more sensitive than the carbazol method and by applying microtit er plates and measuring with an ELISA reader, a large number of tests can be performed within a short time, thereby facilitating initial vel ocity studies. The test is linear up to a concentration of 2.5 mM D-xy lulose even in the presence of to mM D-xylose and 2 mM D-fructose in t he presence of 10 mM D-glucose. The sensitivity is 25 mu M for xylulos e and 38 mu M for fructose. The test method is insensitive to perturba tions of substances frequently used in isolation procedures such as am monium sulfate, Triton X-100, PEG 6000, sodium dodecyl sulfate, and et hanol in moderate concentrations. (C) 1998 Elsevier Science Inc.