Ethylene, formation from methionine

Elstner EE, Saran M, Bors W and LengfelderE (1978) Oxygen activation in isolated chloroplasts. Mechanism offerredoxin-dependent ethylene formation from methionine. Eur J Biochem 89 61-66... 

Ethylene is now considered to be one of the main plant-hormones involved in fruit development. Many responses formerly believed to result from the presence of auxins are now ascribed to induced ethylene production.425 The biosynthetic pathway for formation of ethylene from methionine, in a wide variety of plant tissues, including shoots of mung bean,426 tomato,427 and pea427 carrot427 and tomato428 roots and the fruits of apple,429,430 tomato,427 and avocado,427 has been elucidated, and is as follows. 

Some microorganisms in culture show methionine-dependent ethylene formation. In studies with Escherichia coli, 2-oxo-4-methylthiobutyrate (KMB) produced from methionine by transamination was suggested as the precursor of ethylene [19], and subsequently a cell-free system which produced ethylene from KMB in the presence of NAD(P)H, EDTA-Fe and oxygen was established [20]. An enzyme which catalysed a similar ethylene-forming activity was purified from Cryptococcus albidus [15]. The purified enzyme of molecular mass 62 kDa turned out to be NADH EDTA-Fe oxidoreductase. The proposed mechanism involves reduction of EDTA-Fe to EDTA-Fe by the enzyme, reduction of oxygen to superoxide by EDTA-Fe, of hydrogen peroxide to hydroxyl radical, and oxidation of KMB by hydroxyl radical to ethylene. However, an extensive physiological evaluation of this enzyme must be done before it can... 

The formation of ethylene is often induced by the hormone auxin (Chapter 30), which stimulates activity of the synthase that forms 1-aminocyclopropane-1-carboxylate (ACC) from S-adenosyl methionine (Eq. 14-27, step j Fig. 24-16).320a/b Although ACC has... 

The degradation of methionine in its role of ethylene production leads to CO2, formate, and ethylene from the Ci, C2, and Ca,4, respectively, of the a-aminobutyryl moiety. The fate of the methylthio fragment is unclear but it is suggested that it is utilized to resynthesize methionine by transfer to some four-carbon acceptor (Adams and Yang, 1977). 

Reactions between the sulfur-containing amino acids cysteine and methionine (Fig. 2.18) and rufhenium(II) arene anticancer complexes are of much interest in view of the strong influence of sulfur amino acids on the intracellular chemistry of platinum drugs, their involvement in detoxification and resistance mechanisms [100]. We found [101] that [(ri -biphenyl)Ru(en)Cl][PF 5] reacts slowly with the thiol amino add L-cysteine in aqueous solution at 310 K, pH 2-5, and only to about 50% completion at a 1 2 mM ratio. Reactions appeared to involve aquation as the first step followed by initial formation of 1 1 adducts via substitution of water by S-bound or O-bound cysteine. Two dinuclear complexes were also detected as products from the reaction. In these reactions half or all of the chelated ethylene-diamine had been displaced and one or two bridging cysteines were present The unusual cluster species (biphenyl) Ru g was also formed espedaUy at higher cysteine concentrations. The reaction was suppressed in 50 mM triethylammo-nium acetate solution at pH > 5 or in 100 mM NaCl suggesting that thiols may not readily inactivate Ru(II)-en arene complexes in blood plasma or in cells. Similarly, reactions with the thioether sulfur of methionine appeared to be relatively weak. Only 27% of [(r -biphenyl)Ru(en)Cl][PF5] reacted with L-methionine (L-MetH) at an initial pH of 5.7 after 48 h at 310 K, and gave rise to only one adduct [(ri -biphenyl) Ru(en) (i-MetH -S)]. ... 

It s amazing, but the simplest of all alkenes, ethylene, is an important plant hormone. Among other functions, ethylene acts to promote ripening of fruit. Moreover, production of ethylene is autocatalytic that is, a little ethylene induces the formation of more from the amino acid methionine, and its effects are magnified. Accordingly, fruits such as tomatoes and bananas are now typically shipped green in well-ventilated containers so they will arrive unspoiled. Ripening can then be started by exposure to ethylene. 

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