J. Biol. Chem., Vol. 261, Issue 25, 11538-11543, 09, 1986
Trapping of an intermediate in the reaction catalyzed by 5-oxoprolinase
AP Seddon and A Meister
Bacterial 5-oxoprolinase is composed of two protein components: Component
A, which catalyzes 5-oxoproline-dependent ATP-hydrolysis and Component B,
which couples the hydrolysis of ATP with the decyclization of 5-oxoproline
to form glutamate (Seddon, A. P., Li, L., and Meister, A. (1984) J. Biol.
Chem. 259, 8091-8094). Studies on this unusual enzyme system have led to
evidence that an intermediate is formed by Component A. Application of the
isotope-trapping method demonstrated an activated 5-oxoproline
intermediate, whose formation requires ATP, Mg2+, and Component A. The
amount of ATP-dependent trapping was close to the number of enzyme active
sites. The intermediate formed by Component A was shown to be reducible by
potassium borohydride to proline in low yield; when Component B was added,
the formation of proline was abolished. Treatment of reaction mixtures
containing Component A, 5-oxoproline, and [gamma-32P] ATP with diazomethane
led to appearance of a 32P-labeled compound (found on thin layer
chromatography), whose formation was significantly reduced when Component B
was present. The new compound, which is labile, breaks down to form
dimethyl[32P]phosphate. The total amount of dimethyl[32P]phosphate formed
after breakdown is close to the number of active sites of Component A. The
data are consistent with the conclusion that a phosphorylated form of
5-oxoproline is formed by Component A and suggest that Component B is
required for conversion of this intermediate to glutamate.