Ethylene is a plant growth regulator with potent effects throughout plant growth and development, from seed germination through fruit ripening and senescence and death of the plant. Other plant hormones affect the key regulatory step leading to the synthesis of ethylene in plants. Thus, the biosynthesis of ethylene presents a very complicated picture. The enzyme which carries out the final biosynthetic step is present in extremely small amounts and has eluded expert plant biochemists for years. This project funds a short term project to purify and identify this key plant enzyme. Both the phytohormones indole-3-acetic acid and brassinosteroid specifically affect the conversion of S- adenosylmethionine (SAM) to 1-aminocyclopropane-1-carboxylic acid (ACC), the key reaction controlling the production of ethylene. Despite ethylene's role in diverse plant physiological processes, the major features of control of its formation from SAM via ACC within the plant and how it acts have not been established. The study of ACC synthase (the rate limiting enzyme which catalyzes the reaction between SAM and ACC) and how phytohormones affect its level in tissues have been hampered by the inability to obtain purified enzyme and thus be able to detect specific changes in mRNA formation or stability which could account for the elevation in ACC synthase activity. This study focuses on the further development of the present purification scheme for obtaining purified enzyme and also to characterize it. The enzyme being purified is ACC synthase from etiolated mung bean hypocotyl tissue which has been hormonally treated to elevate enzyme levels. Purification will involve chromatography on phenyl sepharose, hydroxylapatite and anion exchange columns. The purified enzyme will be characterized by denaturing gel electrophoresis and isoelectric focusing. Kinetic properties and coenzyme content will also be analyzed. Once this project is complete to study the regulation of ACC synthase can be attempted and how other plant hormones affect transcriptional control of this key enzyme can be learned.***//
