Crystallographic studies of the mechanism of xylose isomerase. Academic Article uri icon

Overview

abstract

  • The mechanism of xylose isomerase (EC 5.3.1.5) has been studied with X-ray crystallography. Four refined crystal structures are reported at 3-A resolution: native enzyme, enzyme + glucose, enzyme + glucose + Mg2+, and enzyme + glucose + Mn2+. One of these structures (E.G.Mg) was determined in a crystal mounted in a flow cell. The other structures were equilibrium experiments carried out by soaking crystals in substrate containing solution. These structures and other studies suggest that, contrary to expectation, xylose isomerase may not use the generally expected base-catalyzed enolization mechanism. A mechanism involving a hydride shift is consistent with the structures presented here and warrants further investigation. Additional evidence in support of a hydride shift comes from comparing xylose isomerase with triosephosphate isomerase which is known to catalyze an analogous reaction via an enediol intermediate. Evidence is presented that suggests that aldose-ketose isomerases can be divided into two groups. Phospho sugar isomerases generally do not require a metal ion for activity and show exchange of substrate protons with solvent. In contrast, simple sugar isomerases all require a metal ion and show very low solvent exchange. These observations are rationalized on the basis of the need for stereospecific sugar binding.

publication date

  • September 5, 1989

Research

keywords

  • Aldose-Ketose Isomerases
  • Carbohydrate Epimerases

Identity

Scopus Document Identifier

  • 0024962364

Digital Object Identifier (DOI)

  • 10.1021/bi00444a022

PubMed ID

  • 2510821

Additional Document Info

volume

  • 28

issue

  • 18