Аннотация
p-Aminobenzoate, a component of the vitamin folate, is one of seven
compounds derived from the aromatic precursor chorismate in Escherichia
coli. Historically the gene products of pabA and pabB were assumed
to be sufficient for de novo p-aminobenzoate biosynthesis. Recent
studies, however, have shown that these proteins, as nonidentical
subunits of a single enzyme, act on chorismate to form a diffusible
intermediate, most likely 4-amino-4-deoxychorismate. This intermediate
is then converted to p-aminodeoxychorismate lyase (Nichols, B. P.,
Seibold, A. S., and Doktor, S. Z. (1989) J. Biol. Chem. 264, 8597-8601).
Here we describe partial characterization of the intermediate and
the purification of aminodeoxychorismate lyase 4100-fold to near
homogeneity. Further purification of this enzyme by high pressure
liquid chromatography permitted isolation of a pure sample that
yielded N-terminal sequence. A 64-fold redundant oligonucleotide
probe was used to identify a lambda clone containing the gene encoding
aminodeoxychorismate lyase. The aminodeoxychorismate lyase gene,
designated pabC, was mapped to 25 min on the E. coli chromosome
and lies on a 7.5-kilobase pair EcoRI fragment. A strain harboring
a pACYC184 recombinant containing pabC overproduced aminodeoxychorismate
lyase activity 77-fold.
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