Purification and Molecular Analysis of an Extracellular γ-Glutamyl Hydrolase Present in Young Tissues of the Soybean Plant

A polypeptide present in intercellular wash fluids of young leaves ofGlycine maxhas been purified to electrophoretic homogeneity. The protein has been identified as γ-glutamyl hydrolase (GGH) based on the shared homology with a recently cloned cDNA from rat. The enzyme is present within the extracellular space of young leaves and a portion is bound to the cell wall. Northern and Western analysis confirm that this polypeptide is expressed only in young (1-15 d old) leaf, stem and root tissue and is therefore expressed under a strict developmental program. The primary sequence of γ-glutamyl hydrolase shares amino acid identity with a cDNA clone from rat and two partially sequenced cDNAs fromArabidopsis.Although the completein vivofunction of γ-glutamyl hydrolase in plants is unclear, it is known that the protein plays a critical role in folate metabolism and therefore likely in meeting the physiological demands of growing plant tissues.