Locating Active-site Hydrogen Atoms in D-Xylose Isomerase: Time-of-Flight Neutron Diffraction.

Journal Article · Sun Jan 01 04:00:00 EST 2006 · Proceedings of the National Academy of Sciences

OSTI ID:930840

Bunick, G J ^[1]

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1. ORNL

Time-of-flight neutron diffraction has been used to locate hydrogen atoms that define the ionization states of amino acids in crystals of D-xylose isomerase. This enzyme, from Streptomyces rubiginosus, is one of the largest enzymes studied to date at high resolution (1.8 ) by this method. We have determined the position and orientation of a metal ion-bound water molecule that is located in the active site of the enzyme; this water has been thought to be involved in the isomerization step in which D-xylose is converted to D-xylulose or D-glucose to D-fructose. It is shown to be water (rather than a hydroxyl group) under the conditions of measurement (pH 8.0). Our analyses also reveal that one lysine probably has an -NH2 terminal group (rather than NH3+). The ionization state of each histidine residue was also determined.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: ORNL LDRD Seed-Money
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 930840
• Journal Information: Proceedings of the National Academy of Sciences, Journal Name: Proceedings of the National Academy of Sciences Journal Issue: 22 Vol. 103; ISSN PNASA6; ISSN 0027-8424
• Country of Publication: United States
• Language: English

Related Subjects

08 HYDROGEN
AMINO ACIDS
ATOMS
ENZYMES
HISTIDINE
HYDROGEN
IONIZATION
ISOMERIZATION
LYSINE
NEUTRON DIFFRACTION
ORIENTATION
RESIDUES
RESOLUTION
STREPTOMYCES
WATER
amino acid ionization states
deuterium
enzyme mechanism
hydrogen in proteins
proton transfer
x-ray diffraction