Developmentally regulated expression of a peptide : N-Glycanase during germination of rice seeds (Oryza sativa) and its purification and characterization

Peptide:N-glycanase (PNGase; EC 3.5.1.52) activity was detected in dormant rice seeds (Oryza sativa) and the imbibed rice grains. Time-course studies revealed that the enzyme activity remained almost constant until about 30 h after imbibition in both of endosperm- and embryo tissue-containing areas, and started to increase only in growing germ part, reached a peak at about 3-day stage, followed by a gradual decrease concomitant with a sharp incre ase in the coleoptile. The specific activity increased about g-fold at abou t 3-day stage. PN-Gase was purified to electrophoretic homogeneity from the extracts of germinated rice seeds at 24 h, and the apparent molecular weig ht of the purified enzyme, estimated by SDS-polyacrylamide gel electrophore sis (SDS-PAGE), was about 80,000. The purified enzyme was designated PNGase Os to denote its origin. The N-terminal sequence of the 10 residues was de termined to be SYN-VASVAGL, The purified PNGase Os in SDS-PAGE appeared as a rather broad band, consistent with the presence of multiple glycoforms as indicated by chromatographic behavior on a Sephadex G-75 column. PNGase ex pressed in coleoptile under anoxia condition was also purified, and both of the purified enzymes were found to exhibit very similar, if not identical, electrophoretic mobility in SDS-PAGE. PNGase Os exhibited a broad pH-activ ity profile with an optimum of 4-5 and, interestingly, was significantly in activated by K+ and Na+ at near the physiological concentration, 100 mM. Th ese results are discussed in relation to other work.