Purification and molecular analysis of an extracellular gamma-glutamyl hydrolase present in young tissues of the soybean plant.

A polypeptide present in intercellular wash fluids of young leaves of Glycine max has been purified to electrophoretic homogeneity. The protein has been identified as gamma-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 gamma-glutamyl hydrolase shares amino acid identity with a cDNA clone from rat and two partially sequenced cDNAs from Arabidopsis. Although the complete in vivo function of gamma-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.