Ureide metabolism in leaves of nitrogen-fixing soybean plants

In leaf pieces from nodulated soybean (Glycine max [L] Merr cv Maple Arrow) plants, [14C]urea-dependent NH3 and 14CO2 production in the dark showed an approximately 2:1 stoichiometry and was decreased to less than 11% of the control (12-19 micromoles NH3 per gram fresh weight per hour) in the presence of 50 millimolar acetohydroxamate, a urease inhibitor. NH3 and CO2 production from the utilization of [2-14C] allantoin also exhibited a 2:1 stoichiometry and was reduced to a similar extent by the presence of acetohydroxamate with a concomitant accumulation of urea which entirely accounted for the loss in NH3 production. The almost complete sensitivity of NH3 and CO2 production from allantoin and urea metabolism to acetohydroxamate, together with the observed stoichiometry, indicated a path of ureide assimilation (2.0 micromoles per gram leaf fresh weight per hour) via allantoate, ureidoglycolate, and glyoxylate with the production of two urea molecules yielding, in turn, four molecules of NH3 and two molecules of CO2.