Ethylene-forming enzyme

When subjected to drought stress, excised wheat Triticum aestivum L.) leaves increase ethylene production as a result of an increased synthesis of ACC 71 and an increased activity of the ethylene-forming enzyme (EFE) which catalyzes the conversion of ACC 71 to ethylene. Rehydratation to relieve water stress reduces EFE activity to levels similar to those in non-stressed tissue. Pretreatment of the leaves with N-benzyladenine (BA) 75 or indole-3-acetic acid lAA 76 prior to drought stress caused further increase in ethylene production. Conversely, pretreatment of wheat leaves with abscisic acid ABA 77 reduced ethylene production to levels of non-stressed leaves, accompanied by a decrease in ACC 71 content, Eq. (29). 

Ververidis, P. John, P. (1991). Complete recovery in vitro of ethylene-forming enzyme activity. Phytochemistry 30, 725-727. 

Fig. 1. Ethylene biosynthesis. The numbered enzymes are (1) methionine adenosyltransferase, (2) ACC (l-aminocyclopropane-l-carboxylic acid) synthase, (3) ethylene forming enzyme (EFE), (4) 5 -methylthio-adenosine nucleosidase, (5) 5 -methylthioribose kinase. Regulation of the synthesis of ACC synthase and EFE are important steps in the control of ethylene production. ACC synthase requires pyridoxal phosphate and is inhibited by aminoethoxy vinyl glycine EFE requires 02 and is inhibited under anaerobic conditions. Synthesis of both ACC synthase and EFE is stimulated during ripening, senescence, abscission, following mechanical wounding, and treatment with auxins.

Ethylene plays an important role in a number of plant developmental processes, including senescence and abscission of leaves and flowers, responses to wounding, and the ripening of climacteric fruits (Abeles, 1973). In each case ethylene is produced from methionine (Fig. 1). The two enzymes specific to the pathway, ACC synthase and ethylene forming enzyme, increase in activity in response to wounding and during ripening,... 

Fig. 5. Activity of ethylene forming enzyme (ACC oxidase) in wounded leaves of transgenic tomato plants containing 0, 1, or 2 pTOM 13 anti-sense genes (after Hamilton et at., 1990).

Comparison of the predicted amino acid sequence of the protein encoded by pTOM 13 with the sequence of flavanone 3-hydroxylase showed considerable similarity (A. Prescott and C. Martin, personal communication, cited in Hamilton etal., 1990). This is particularly interesting, since it has been suggested that the conversion of ACC to ethylene might involve a hydroxylation reaction (Yang, 1985). Armed with this information and using conditions developed for extraction and purification of flavanone 3-hydroxylase, Ververidis John (1991) showed that it is possible to solubilise the ethylene forming enzyme from plants and retain full... 

Fig. 7. Ethylene forming enzyme activity in transformed yeast cells at different stages of the culture cycle. A, Yeast cell number. EFE activity in yeast cells with ( ) and without (O) the reconstructed pTOM 13 cDNA (after Hamilton et al., 1991).

Since earlier studies on synthesis, activity and regulation of ethylene forming enzyme were carried out with excised tissue slices or discs, the... 

Hamilton, A.J., Bouzayen, M. Grierson, D. (1991). Identification of a tomato gene for the ethylene forming enzyme by expression in yeast. Proceedings of the National Academy of Sciences (USA) 88, 7334-7. 

Biochemical reactions of l-amino-2-ethylcyclopropane-l-carboxylic acid showed strong stereoselectivity. Thus, ring-opening to 2-ketohexanoate was observed only with the (IS, 2S)-isomer (505) . On the other hand, cycloelimination to give butene by the ethylene forming enzyme in apples or pea epicotyls was performed preferentially with allocoronamic acid (649), the (IR, 2S)-isomer Pea epicotyl enzyme (cell-free system) catalyzed the formation of 1-butene for all stereoisomers (i.e. 505 and 649)" ... 

Iron is important in plants not only because of its role in fundamental processes such as photosynthesis, respiration, nitrogen fixation, and DNA synthesis, but also because of its involvement in key enzymes of plant hormone synthesis, such as lipoxygenases and ethylene-forming enzymes. Despite the fact that iron represents 4—5% of the total solid mineral composition of soils, it is generally present in soils in a poorly soluble form, and... 

ACC synthase, followed by conversion to ethylene by ACC oxidase (formerly called ethylene-forming enzyme or EFE) [75]. ACC synthase is a soluble enzyme, while ACC oxidase is located on the tonoplast [19]. 

Fig. 1. Bi-functional reaction mechanism of ethylene-forming enzyme from Pseudomonas syringae proposed by Fukuda et al. (1992). Reproduced by permission.

It is generally accepted that cyanobacterial TCA cycle is not very active under phototrophic conditions. A recent study further proved that it operates in a bifurcated way [112]. However, the bifurcated pattern switches to a dominantly cyclic pattern by introducing an ethylene-forming enzyme from Pseudomonas. Ethylene can be sustainably and efficiently produced from 2-oxoglutarate while also activating the TCA cycle metabolism. The enhanced flux via the remodeled TCA is 37% of the total fixed carbon which is higher than the 13% found in wild type. This result indicates that the metabolic malleability of the cyanobacterial TCA cycle depends on what it produces. 

Figure 3. Biosynthetic transformations mediated by non-heme iron proteins related to the ethylene-forming enzyme.

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