Ethylene production from methionine

Abstract

1. A new reaction is described in which ethylene is formed from the Cu+-catalysed breakdown of methionine in phosphate buffer at 300 in air. Some of the other products of the reaction are methionine sulphone, methionine sulphoxide, homocysteic acid, homocystine, acrolein, dimethyl disulphide, methanethiol, ethyl methyl sulphide, methane and ethane. These are considered to be produced in different reaction pathways. The formation of ethylene in a model system in which Cu+ catalyses the breakdown of peroxidated linolenic acid has been described (Lieberman & Mapson, 1964). It was proposed that the biosynthesis ofethylene may proceed through an analogous system catalysed by a copper enzyme. Recent experiments, however, suggest that ethylene in tissues may arise from more than one source. For example, an analysis of particulate fractions, isolated from apples, shows that at least two types of compounds are present which can yield ethylene in the Cu+-catalysed system. The first is associated with the fat-soluble constituents of the cell and the second with the water-soluble constituents.Search for other precursors of ethylene has led to the finding that L-methionine, in reaction with the cuprous generating system, also forms ethylene. It is shown below that methionine and related substances are unique in their ability to form relatively large quantities of ethylene in a model system. The present paper describes characteristics of this ethylene-forming system, demonstrates that ethylene is derived from C-3 and C-4 of methionine, and suggests a mechanism for the reaction. MATERIALS AND METHODSModel 8y8tem. The model system consisted of L-methionine (1 mM), CU2+ (1.0 or 0-1 mm), ascorbate (10mm) and phosphate buffer, pH6.8 (60mm). Components of the 15 model system were contained in 25 ml. flasks sealed with one-hole rubber stoppers containing clamped capillary tubes. The flasks were incubated at 300 in a water bathshaker and internal atmospheres above the reaction mixture were sampled periodically with gas-tight syringes. Corrections were made to account for the increase in gas volume resulting from this sampling technique.Gas analysis. Gases produced in the reaction were determined by gas chromatography. Alumina or silicone (30% silicone oil on Celite) columns and a flame-ionization detector were used to determine ethylene. Details of the complete system have been described by Meigh, Norris, Craft & Lieberman (1960). Acrolein, ethyl methyl sulphide, dimethyl sulphide, dimethyl disulphide and methanethiol were detected on a capillary column (80ft. x 0-015in. diam.) at 150 with di-(2-cyanoethyl) ether as stationary phase, with an enrichment trap cooled in liquid 02 to first concentrate the gases. The vapours were subsequently released from the trap by passing an electric current through the trap.Methional. This compound was prepared from acrolein and methanethiol by the method described by Pierson, Giella & Tishler (1948

Mechanism of Auxin-induced Ethylene Production

“…Yang (30) speculated that the pea system may be a peroxidase and later Mapson and Wardale (24) further characterized the cauliflower enzyme system and concluded that the enzyme may indeed be a peroxidase. Although methionine appears to be a substrate for the production of ethylene in pea tissue treated with IAA (8,22), peroxidase only produces ethylene from methional or a-keto-y-methylthiobutyric acid (21), but not from S-adenosyl methionine or methionine. Furthermore, there is evidence that methional and the a-keto-analogue are not converted to ethylene as readily as methionine in vivo, and in addition C-2 of methionine is not converted to CO, in vivo (8), whereas peroxidase converts C-2 of the a-ketoanalogue to COa in vitro (31).…”

Stimulation of Ethylene Production in Apple Tissue Slices by Methionine

“…The first utilizes linlolenate as substrate (1) and the second requires methionine, ethioninie, or the a-hydroxy analogue of imethionine as substrate (2). Both …”

Precursors of Ethylene

“…The conversion of methionine to etlhylene in model systems (8,19) and in plant tissues (2,9) has been demonstrated. In the FMN-light mediated model system (19), it has been established that methionine is converted to ethylene via methional (,a-methylthiopropionaldehyde) as an intermediate.…”