Evaluation of the Role of Methional, 2-Keto-4-methylthiobutyric Acid and Peroxidase in Ethylene Formation by Escherichia coli

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Abstract
During growth of E. coli strain SPA O in the presence of methionine, an intermediate accumulates in the medium. This intermediate reacts with 2,4-dinitrophenylhydrazine and can be degraded to ethylene either enzymically or photochemically, the latter being stimulated by the addition of a flavin. The pH optimum for the photochemical degradation of this intermediate and 2-keto-4-methylthiobutyric acid (KMBA) is pH 3; the optimum for methional is pH 6. The enzyme which converts the intermediate to ethylene also converts KMBA to ethylene and has many of the properties of a peroxidase including inhibition by catalase, cyanide, azide and anaerobiosis. The enzyme which synthesizes the intermediate is not known but requires O2 and pyridoxal phosphate. A pathway for ethylene biosynthesis is proposed in which methionine is converted to KMBA which can be degraded either by peroxidase or in a flavin-mediated photochemical reaction. Its relevance to the properties of other ethylene-producing bacteria and to the proposed pathway of ethylene release by higher plants is discussed.

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