Urea is a product of ureidoglycolate degradation in chickpea. Purificationand characterization of the ureidoglycolate urea-lyase

A ureidoglycolate-degrading activity was analyzed in different organs of ch ickpea (Cicer nrietinum). 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-deg rading activity that has been purified to homogeneity from any photosynthet ic organism. Only one ureidoglycolate-degrading activity was found during t he 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 turnove r 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 w ith K-m values of 6 and 10 muM in the presence or absence of Mn2+, respecti vely Optimum pH was between 7 and 8 and maximum activity was found at tempe ratures above 70 degreesC, the enzyme being extremely stable and resistant to heat denaturation. The activity was inhibited by EDTA and enhanced by se veral 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 glyoxylat e and urea. This is the first time that such an activity is detected in pla nt tissues. A possible function for this activity and its implications in t he context of nitrogen mobilization in legume plants is also discussed.