Enzymic Degradation of Allantoate in Developing Soybeans

Abstract

A Mn2-dependent enzymic breakdown of allantoate has been detected in crude and partially purified extracts of developing soybeans. The products detected were CO2, NH3, glyoxylate, labile glyoxylate derivatives, and low levels of urea. Urea is initially produced at less than 10% the rate of urease-independent CO2 release indicating that the activity is not allantoate amidinohydrolase (i.e. urea is not directly cleaved off allantoate). The urease-independent CO2 releasing activity has an apparent K,. of 1.0 nillimolar for allantoate. Ethylenediaminetetraacetate, borate, and acetohydroxamate (all at 10 millimolar) inhibit the enzymic production of NH3, C02, and labile glyoxylate derivatives from allantoate. However, the potent urease inhibitor, phenyl phosphordiamidate does not inhibit CO2 and NH3 release indicating that the action of acetohydrexamate is not due to its inhibition of urease. That the allantoatedegrading activity was more than 5-fold greater in seed coats than in embryos is consistent with the data of Rainbird et al. (Plant Physiol 1984 74: 329-334) which indicate that available ureides are metabolized before reaching the embryo. 2-Ethanolthio, 2'-ureido, acetic acid (NH2COHNCHCO2HSCH2CH20H), the first allantoate-derived product detected by HPLC analysis, is an addition product of mercaptoethanol with an unidentified enzymically produced ureido intermediate that is not derived from ureidoglycolate or oxalurate.

Asparagine and Boric Acid Cause Allantoate Accumulation in Soybean Leaves by Inhibiting Manganese-Dependent Allantoate Amidohydrolase

“…This is consistent with the previously reported Mn requirement for allantoate amidohydrolase activity from soybean seed coats and developing beans (23,24). Chelators and other metal-binding agents, like EDTA, acetohydroxamate, and boric acid, had potent inhibitory effects on the activity of leaf allantoate amidohydrolase (21) (Fig.…”

“…However, despite the decline in ureide transport, a substantial increase in allantoate concentration is observed in leaves of nodulated soybeans exposed to ammonium nitrate 1 (13,24). This accumulation of allantoate could be explained either by ureide formation in plant tissues other than nodules (stimulated by the alternative source of nitrogen) or by inhibition of ureide degradation in leaves.…”

Ureide Catabolism of Soybeans

“…These results confirm the results reported by Shelp and Ireland (14). AHA, a urease inhibitor and metal chelator (26), also inhibits allantoate-dependent glyoxylate production in partially purified extracts of soybean seed coats (27). Data (Fig.…”

“…The amidinohydrolase is generally termed allantoicase and has been proposed to be present in soybeans (14). On the other hand we have previously demonstrated evidence for ALAH in extracts of developing soybean (27). Several different reports have focused on plant ALN metabolism, but no report has conclusively elucidated the entire pathway of catabolism.…”

“…This result strongly suggested that the nitrogen of ALN was at least partially catabolized without urease action. Winkler et al (27) provided evidence for an Mn2+-dependent allantoate amidohydrolase in developing soybeans and seed coats. In experiments where urease was completely inhibited by PPD, (one of the most potent urease inhibitors known [17]) the release of NH14 and CO2 from allantoate was unaffected.…”