Hydrogen Location in Stages of an Enzyme-Catalyzed Reaction: Time-of-Flight Neutron Structure of d-X
June 27th, 2008 | by admin |Hydrogen Location in Stages of an Enzyme-Catalyzed Reaction: Time-of-Flight Neutron Structure of d-Xylose Isomerase with Bound d-Xylulose.
The time-of-flight neutron Laue technique has been used to determine the location of hydrogen atoms in the enzyme d-xylose isomerase (XI). The neutron structure of crystalline XI with bound product, d-xylulose, shows, unexpectedly, that O5 of d-xylulose is not protonated but is hydrogen-bonded to doubly protonated His54. Also, Lys289, which is neutral in native XI, is protonated (positively charged), while the catalytic water in native XI has become activated to a hydroxyl anion which is in the proximity of C1 and C2, the molecular site of isomerization of xylose. These findings impact our understanding of the reaction mechanism.
Kovalevsky AY, Katz AK, Carrell HL, Hanson L, Mustyakimov M, Fisher SZ, Coates L, Schoenborn BP, Bunick GJ, Glusker JP, Langan P.
M888, Bioscience Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, Pennsylvania 19111-2497, Chemistry Department, University of Toledo, Toledo, Ohio 43606, and Chemistry Department, University of Tennessee, Knoxville, Tennessee 37996 langan_paul@lanl.gov.