DXP Reductoisomerase: Reaction of the Substrate in
Pieces Reveals a Catalytic Role for the Nonreacting Phosphodianion
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Abstract
The
role of the nonreacting phosphodianion group of 1-deoxy-d-xylulose-5-phosphate (DXP) in catalysis by DXP reductoisomerase
(DXR) was investigated for the reaction of the “substrate in
pieces”. The truncated substrate 1-deoxy-l-erythrulose
is converted by DXR to 2-<i>C</i>-methylglycerol with a <i>k</i><sub>cat</sub>/<i>K</i><sub>m</sub> that is 10<sup>6</sup>-fold lower than that for DXP. Phosphite dianion was found
to be a nonessential activator, providing 3.2 kcal/mol of transition
state stabilization for the truncated substrate. These results implicate
a phosphate-driven conformational change involving loop closure over
the DXR active site to generate an environment poised for catalysis