Comparison of Enzymatic Properties and Gene Expression Profiles of Two Tuberonic Acid Glucoside β-Glucosidases from Oryza sativa L.

摘要

Rice tuberonic acid glucoside-hydrolyzing β-glucosidase (OsTAGG) produces physiologically active tuberonic acid (TA) from its glucoside (TAG). We have previously reported the identification and some properties of OsTAGG1. Here, we describe the isolation and enzymatic properties of another OsTAGG isozyme (OsTAGG2). OsTAGG2 was purified from rice by seven purification procedures with a 2,800-fold purification. Like OsTAGG1, the purified OsTAGG2 migrated as two bands with molecular masses of 40 and 26 kDa on SDS-PAGE. Results from N-terminal sequencing and peptide mass fingerprinting of both polypeptides suggested that both bands were derived from a single polypeptide. The Km and Vmax values of OsTAGG2 toward TAG were 146 μM and 38.0 μmol/min/mg, and were 4.6-fold and 2.6-fold higher than those of OsTAGG1, respectively. OsTAGG2 as well as OsTAGG1 preferentially hydrolyzed TAG among several natural glucosides used in this study. Quantitative real-time reverse transcriptase-mediated PCR analysis revealed that OsTAGG1 and OsTAGG2 are differentially expressed in response to wounding; the expression of OsTAGG1 is down-regulated, whereas that of OsTAGG2 is up-regulated by wound treatment.