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J. Bacteriol., May 1997, 3110-3115, Vol 179, No. 10
JR Allen and SA Ensign
Epoxide carboxylase from Xanthobacter strain Py2 catalyzes the reductant-
and NAD+-dependent carboxylation of aliphatic epoxides to beta-keto acids.
Epoxide carboxylase from Xanthobacter strain Py2 has been resolved from
cell extracts by anion-exchange chromatography into three protein
components, designated I, II, and III, that are obligately required for
functional reconstitution of epoxide carboxylase activity. Component II has
been purified to homogeneity on the basis of its ability to complement
components I and III in restoring epoxide carboxylase activity. Purified
component II had a specific activity for epoxide carboxylation of 41.8 mU x
min(-1) x mg(- 1) when components I and III were present at saturating
levels. The biochemical properties of component II reveal that it is the
flavin- containing NADPH:disulfide oxidoreductase that was recently shown
by other means to be associated with epoxide degradation activity in
Xanthobacter strain Py2 (J. Swaving, J. A. M. de Bont, A. Westphal, and A.
Dekok, J. Bacteriol. 178:6644-6646, 1996). The rate of epoxide
carboxylation was dependent on the relative concentrations of the three
carboxylase components. At fixed concentrations of two of the components,
epoxide carboxylation rates were saturated in a hyperbolic fashion by
increasing the concentration of the third variable component.
Methylepoxypropane has been characterized as a time- dependent,
irreversible inactivator of epoxide carboxylase activity that is proposed
to be a mechanism-based inactivator of the enzyme. The addition of
component I, but not that of component II or III, to
methylepoxypropane-inactivated cell extracts restored epoxide carboxylase
activity, suggesting that component I contains the epoxide binding and
activation sites.
Copyright © 1997, American Society for Microbiology
Characterization of three protein components required for functional reconstitution of the epoxide carboxylase multienzyme complex from Xanthobacter strain Py2
Department of Chemistry and Biochemistry, Utah State University, Logan 84322-0300, USA.
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