Identification of oligopeptidase B in higher plants. Purification and characterization of oligopeptidase B from quiescent wheat embryo, Triticum aestivum.

Proteolytic enzymes in general, and cysteine proteases in particular, play key roles in seed germination and early seedling growth. However, the precise mechanism by which the serine proteases are regulated remains unclear. Trypsin-like activity was detected in wheat germ (quiescent embryo) and this activity increased in the germinating embryo. In this work, a trypsin-like serine protease expressed in wheat germ was purified to homogeneity by chromatography through DEAE-cellulose, phenyl-Sepharose, Ultrogel AcA-34 and Blue-Sepharose. The molecular mass of the enzyme was estimated to be 81 kDa by SDS-PAGE under reducing conditions. Amino acid analysis of the peptides generated following digestion of the enzyme with lysyl endopeptidase indicated that the enzyme is a plant homologue of Escherichia. coli oligopeptidase B. The subsite specificity of the enzymes differ, although both enzymes hydrolyze synthetic substrates and model peptides at the carboxyl side of basic amino acids. The wheat enzyme is more sensitive to leupeptin and antipain than the E. coli emzyme. These results provide the basis for characterizing plant oligopeptidase B and contribute to our understanding of its role in the early development of seedlings.