Content area
Abstract
Soybeans and other tropical legumes assimilate fixed nitrogen into ureides. The first and last stages of ureide biosynthesis have been well studied; however, the intermediate reactions, whereby IMP is converted to xanthine, are still poorly understood. A soluble phosphatase (ACP) from soybean root nodules was purified which exhibits highest specificity for 5$\sp\prime$-nucleotides and is postulated to dephosphorylate 5$\sp\prime$-XMP and/or 5$\sp\prime$-IMP in the intermediate reactions of ureide biosynthesis. A cDNA encoding ACP was isolated, and the mRNA was shown to be dramatically nodule-enhanced and developmentally regulated in a manner consistent with a role in ureide biosynthesis. The enzymatic properties of ACP were confirmed by heterologous expression in Pichia pastoris. The relationship of the nodule ACP to plant phosphatases, vegetative storage proteins, and the HAD superfamily of alpha-beta hydrolases is discussed.
