Recovery of Ethylene Forming Enzyme from Green Pea Pods

Ethylene Forming Enzyme (EFE) is the enzyme that catalyses the final step in the biosynthesis of ethylene (Kende, 1990; Yang etal., 1990; Yang and Hoffinan, 1984). The site of location of this enzyme in the plant cell is still unknown with certainty.' Mattoo and Lieberman (1977) suggested that it is localised in a cell wall-cell membrane complex. Bouzayen et al., 1990) suggested that there are two sites for EFE location in a plant cell. One of the sites is located on the plasmalemma and is very sensitive to plasmolysis of the cell, and the other site is in the tonoplast and its ethylene-forming ability is not affected by plasmolysis. These authors excluded the cell wall as a possible site for EFE location. Ververidis and John (1990) confirmed the findings of Bouzayens etal.; and also suggested that the actual EFE location depends on the stage of plant growth. Irrespective of the site of EFE location, it had been felt that it could only oxidise 1aminocyclopropane-carboxylic acid (ACC) to ethylene effectively if bound to the membrane, as its activity had not been recovered in vitro (John et al., 1985; Venis, 1984; Porter et al., 1986; Mayne and Kende, 1986). However, Ververidis and John (1991), fully recovered EFE activity in a cell free system from melon (Cucurnis melo) fruits. Other cell free systems have been reported to oxidise ACC to ethylene, but all the systems have a very high K,„ for ACC in the plant and this rules out the possibility of such systems being operative in the plant systems in-vivo because of their high Kin values for ACC. (McKeon and Yang, 1984; Stegink et al., 1986; Nielsen et al., 1984; Venis, 1984; Mayak etal., 1981).