J. Biol. Chem., Vol. 263, Issue 19, 9268-9270, Jul, 1988
Preliminary x-ray data on crystals of mandelate racemase
DJ Neidhart, VM Powers, GL Kenyon, AY Tsou, SC Ransom, JA Gerlt and GA Petsko
Department of Chemistry, Massachusetts Institute of Technology, Cambridge 02139.
The recent development of a high-yield expression system and purification
scheme for mandelate racemase has enabled us to produce sufficiently large
quantities of pure enzyme to pursue x-ray crystallographic study. Large,
single crystals of mandelate racemase have been grown from buffered
polyethylene glycol (pH 8.0) in the presence of 10 mM magnesium chloride.
The crystals grow in several habits, and we have identified two distinct
tetragonal space groups in preliminary x-ray diffraction analysis. Crystals
shaped as rectangular plates demonstrate 4/mmm Laue symmetry and systematic
absences consistent with the space group I422. They have cell dimensions of
a = b = 153 A and c = 181 A. Octahedrally shaped crystals of mandelate
racemase display 4/m Laue symmetry and systematic absences consistent with
the space group 14. Cell dimensions for these crystals are a = b = 113 A
and c = 124 A. Based on estimates of Vm and on the measured density of the
1422 form, we suggest that two subunits of mandelate racemase (38,570
daltons/subunit) occupy the asymmetric unit in both crystal forms. Crystals
of both forms diffract to beyond 3.0-A resolution. We are currently
screening for isomorphous heavy-atom derivatives.
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