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J. Biol. Chem., Vol. 275, Issue 30, 22824-22831, July 28, 2000
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From the Interdepartmental Program in Medicinal Chemistry,
University of Michigan, Ann Arbor, Michigan 48109-1065
The enzymes
3-deoxy-D-manno-octulosonic
acid-8-phosphate synthase (KDO8PS) and
3-deoxy-D-arabino-heptulosonic acid-7-phosphate synthase (DAHPS) catalyze analogous condensation reactions between phosphoenolpyruvate and D-arabinose 5-phosphate or
D-erythrose 4-phosphate, respectively. While several
similarities exist between the two enzymatic reactions, classic studies
on the Escherichia coli enzymes have established that DAHPS
is a metalloenzyme, whereas KDO8PS has no metal requirement. Here, we
demonstrate that KDO8PS from Aquifex aeolicus, representing
only the second member of the KDO8PS family to be characterized in
detail, is a metalloenzyme. The recombinant KDO8PS, as isolated,
displays an absorption band at 505 nm and contains approximately 0.4 and 0.2-0.3 eq of zinc and iron, respectively, per enzyme
subunit. EDTA inactivates the enzyme in a time- and
concentration-dependent manner and eliminates the
absorption at 505 nm. The addition of Cu2+ to KDO8PS
produces an intense absorption at 375 nm, while neither Co2+ nor Ni2+ produce such an effect. The
EDTA-treated enzyme is reactivated by a wide range of divalent metal
ions including Ca2+, Cd2+,
Co2+, Cu2+, Fe2+, Mg2+,
Mn2+, Ni2+, and Zn2+ and is
reversibly inhibited by higher concentrations (>1 mM) of
certain metals. Analysis of several metal forms of the enzyme by plasma
mass spectrometry suggests that the enzyme preferentially binds one,
two, or four metal ions per tetramer. These observations strongly
suggest that A. aeolicus KDO8PS is a metalloenzyme in vivo and point to a previously unrecognized relationship between the KDO8PS and DAHPS families.
A Metal Bridge between Two Enzyme Families
3-DEOXY-D-MANNO-OCTULOSONATE-8-PHOSPHATE
SYNTHASE FROM AQUIFEX AEOLICUS REQUIRES A DIVALENT METAL FOR
ACTIVITY*
*
This work was supported by National Institutes of Health
Grant GM 53069 (to R. W. W) and a Natural Sciences and Engineering Research Council of Canada postdoctoral fellowship (to H. S. D).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
To whom correspondence should be addressed: College of Pharmacy,
428 Church St., Ann Arbor, MI 48109-1065. Tel.: 734-764-7366; Fax:
734-763-5633; E-mail: rww@umich.edu.
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