JBC, Vol. 250, Issue 17, 6686-6692, Sep, 1975
5-Oxo-L-prolinase (L-pyroglutamate hydrolase). Purification and catalytic properties
P. Van Der Werf, O. W. Griffith and A. Meister
5-Oxo-L-prolinase, an enzyme that catalyzes the conversion of
5-oxo-L-proline (L-pyroglutamate; L-2-pyrrolidone-5-carboxylate) to
L-glutamate coupled with the cleavage of ATP to ADP and Pi, has been
purified about 1600-fold from rat kidney. Purification was carried out in
the presence of 5-oxo-L-proline which protects the enzyme under a variety
of conditions. An estimate of the molecular weight (about 325,000) was made
by gel filtration on Sephadex G-200. K+ (or NH4+) and Mg2+ were required
for activity. GTP, ITP, CTP, and UTP were much less active than ATP; dATP
was 43% as active as ATP. ADP inhibited and addition of pyruvate kinase and
phosphoenolpyruvate activated the reaction. The enzyme, which is protected
during storage by dithiothreitol, is inhibited by p-hydroxymercuribenzoate,
N-ethylmaleimide, and iodoacetamide. The apparent Km values for
5-oxo-L-proline and ATP are, respectively, 0.05 and 0.17 mM. The pH profile
indicates a broad range of activity from about pH 5.5 to pH 11.2 with
apparent maxima at about pH 7 and pH 9.7. The formation of Pi and glutamate
was equimolar over a wide pH range. When the enzyme was incubated with ATP,
Mg2+, K+, and L-2-imidazolidone-4-carboxylate or L-dihydroorotate, cleavage
of ATP to ADP and Pi occurred, but no cleavage of the imino acid substrates
was observed; when the enzyme was incubated under these conditions with
2-piperidone-6-carboxylate, 4-oxy-5-oxoproline, and 3-oxy-5-oxoproline, the
corresponding dicarboxylic amino acids were formed, but the molar ratio of
Pi to amino acid formation was significantly greater than unity.