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Plant Physiol, February 2001, Vol. 125, pp. 828-834
Urea Is a Product of Ureidoglycolate Degradation in Chickpea.
Purification and Characterization of the Ureidoglycolate
Urea-Lyase1
Alfonso
Muñoz,
Pedro
Piedras,
Miguel
Aguilar, and
Manuel
Pineda*
Departamento de Bioquímica y Biología Molecular,
Campus Rabanales, Edificio C 6, 1a Planta, Universidad de
Córdoba, 14071-Córdoba, Spain
A ureidoglycolate-degrading activity was analyzed in different
organs of chickpea (Cicer arietinum). Activity was
detected in all the tissues analyzed, but highest levels of specific
activity were found in pods, from which it has been purified and
characterized. This is the first ureidoglycolate-degrading activity
that has been purified to homogeneity from any photosynthetic organism. Only one ureidoglycolate-degrading activity was found during the purification. The enzyme was purified 1,500-fold, and specific activity
for the pure enzyme was 8.6 units mg 1, which
corresponds with a turnover number of 1,600 min 1. The
native enzyme has a molecular mass of 180 kD and consists of six
identical or similar-sized subunits of 31 kD each. The enzyme exhibited
hyperbolic, Michaelian kinetics for ( ) ureidoglycolate with
Km values of 6 and 10 µM in
the presence or absence of Mn2+, respectively. Optimum pH
was between 7 and 8 and maximum activity was found at temperatures
above 70°C, the enzyme being extremely stable and resistant to heat
denaturation. The activity was inhibited by EDTA and enhanced by
several bivalent cations, thus suggesting that the enzyme is a
metalloprotein. This enzyme has been characterized as a ureidoglycolate
urea-lyase (EC 4.3.2.3), which catalyzes the degradation of ( )
ureidoglycolate to glyoxylate and urea. This is the first time that
such an activity is detected in plant tissues. A possible function for
this activity and its implications in the context of nitrogen
mobilization in legume plants is also discussed.
1
This work was supported by Dirección
General de Enseñanza Superior e Investigación
Científica (grant no. PB96-0504-C02-02) and Plan Andaluz de
Investigación (grant no. CVI-0115).
*
Corresponding author; e-mail bb1piprm{at}uco.es; fax
34-957-218592.
© 2001 American Society of Plant Physiologists
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