Biochemistry 1994, 33, 1481-1487
1481
Isotopic Exchange plus Substrate and Inhibition Kinetics of D-Xylose Isomerase Do Not Support a Proton-Transfer Mechanism? Karen N. Allen,$ Arnon Lavie,$ Gregory K. Farber,g Arthur Glasfeld,lI Gregory A. Petsko,$ and Dagmar Ringe'J Rosenstiel Basic Medical Sciences Research Center, Brandeis University, 415 South Street, Waltham, Massachusetts 02254-91 10, Department of Chemistry, Reed College, Portland, Oregon 97202, and Department of Chemistry, Pennsylvania State University, I52 Davey Laboratory, University Park, Pennsylvania 16802 Received September 20, 1993; Revised Manuscript Received November 19, 1993"
ABSTRACT: The D-xylose isomerase of Streptomyces olivochromogenes is a Mg2+-or Mn2+-dependentenzyme
that catalyzes the aldose-ketose isomerization of xylose to xylulose or of glucose to fructose. Proton exchange into water during enzyme-catalyzed isomerization of C-2 tritiated glucose a t 15,25 and 55 " C shows
