Expression of a novel ethylene-producing bifunctional fusion enzyme in yeast

The 1-aminocyclopropane-1-carboxylic acid (ACC) dependent ethylene biosynthetic pathway of higher plants was reconstituted in yeast (Saccharomyces cerevisiae). The ACC-dependent ethylene biosynthesis in yeast was catalyzed by a novel bifunctional ACC synthase-ACC oxidase (ACSO) fusion enzyme (Ning Li, Xiang Ning Jiang, Guo Ping Cai and Shang Fa Yang [1996] The Journal of Biological Chemistry 271. 25738-25741). This fusion enzyme ACSO which was further fused to glutathione S-transferase is capable of converting yeast endogenous S-adenosyl-L-methionine (AdoMet) to ethylene. The molecular weight of the fusion enzyme, GST-ACSO, expressed in yeast, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), was 110 kDa. The ethylene production rate of the yeast cell containing GST-ACSO fusion enzyme was determined to be 21.4 pmol hr(-1) per 10(8) cells at 8 h of galactose induction. The level of ACC, produced as an intermediate during the sequential reactions from AdoMet to ethylene, was found to increase gradually after galactose induction. Because ACSO is capable of producing ethylene from the ubiquitous and prevalent AdoMet in the living eukaryotic cell and the method commonly used to measure ethylene is simple, fast, and extremely sensitive (0.03 parts per billion), we anticipate this bifunctional fusion enzyme to be useful in the near future for research in molecular biology, developmental biology, fermentation, and genetic engineering.