Sutwumary. AMethionine can iniduce more thani a 100 % inlcrease in ethylene prodluction by apple tissue slices. The increased amounit of ethvlenie derives from carbolns 3 and 4 of methionine. On4l post-climacteric fruit tissues are stimulated bv iimethionine, and stimulatioin is optimum after 8 months' storage. Copper chelators such as sodium diethvl (lithiocarbam-nate and cuprizone very markedly inhibit ethylene production by tissuie slices. Carbon monoxide does not effect ethylene produiction by the slices. These (lata sluggest that the mechanism for the coniversion of mnethionine to ethylene, in apple tissues, is similar to the previously descriibed model system for pro(duicing ethylene fromii imiethionine and reduced copper. Therefore, it is suggested that one of the ethylene-forming systemis in tissues derives fromii miiethionine and proceeds to ethylene via a copper enzyme system which may be a peroxidase. over inoninfiltrated treatmiienits, of rem,oving the preformiied ethylenie fromii the slices. Inl somiie later experiments air was replacedI by 0,. since it w-as found( that ethylene production by apple slices immiiiiersed in liquid media was stimulated b) O.-Gas Anialy-sis. Gases evolved by the tissue slices were sample(d by syringe anid determined by gas chromatography with a flamiie-ionization detector in a system using either alumiinia or silicolle (30% silicolne oil on celite) colulmniiis (3).T'racer EIxperinients. Tracer studies were carrie(d out with 14C. CH, labeled r-methionine, I)J.-methionine carboxy 4C, DL wlethioninle 2, 14C. or I)! n'ethionine 3, 4, 14C, added to the sucrose-bicarbonate inicubation mlixture. A 2 mil aliquiot of the gases evolved by the apple tissue slices xvas first assaye(l for ethylene onl the gas chromlatograph, and(I then 50 % of the gaseous atmosphere in the incuibation flask was remioved with a 50-nl gas-tight syringe for 14C analy sis.

No abstract

1. Two enzymes were shown to be necessary for the production of ethylene from methional; they were separated from extracts of cauliflower florets by fractionation on Sephadex and other methods. 2. The first enzyme, generating hydrogen peroxide, appears to be similar to the fungal glucose oxidase, for like the latter it is highly specific for its substrate d-glucose. 3. The second enzyme, in the presence of cofactors and peroxide generated by the first enzyme, cleaves methional to ethylene. 4. It was also found that hydrogen peroxide in these reactions may be replaced by hydroperoxide generated from linolenic acid by lipoxidase enzymes. 5. Dihydroxyphenols were shown to have a marked inhibitory effect on these reactions and to account for the initial phase of low activity that is always observed in aqueous extracts prepared from the floret tissue.

1. The formation of ethylene from cauliflower florets is stimulated by the addition of either methionine or its hydroxy analogue. 2. Formation of ethylene from these compounds may also be demonstrated in cell-free extracts, but the most rapid formation is achieved by the addition of methional. 3. Fractionation of such extracts has shown that both particulate and non-particulate fractions are necessary for the formation of ethylene from methionine or its hydroxy analogues, but only the non-particulate fraction is necessary for its formation from methional. 4. A study of this system has shown that the conversion of methional into ethylene requires the presence of two enzyme systems, the first generating peroxide and the second catalysing the conversion of methional into ethylene in the presence of peroxide. 5. The presence of a heat-stable factor in cauliflower extracts that is necessary for the full activity of the enzyme converting methional into ethylene has also been shown. 6. The nature of this factor is at the present unknown; it is not a metal nor is it identifiable with many of the known coenzymes.

The enzyme responsible for the conversion of methionine into a precursor of ethylene in cauliflower florets is a transaminase. The formation of 4-methyl-mercapto-2-oxobutyric acid by this enzyme has been shown. The oxo acid stimulates the synthesis of ethylene when added to floret tissue, and tracer experiments have shown that (14)C is incorporated into ethylene from the labelled oxo acid. The evidence is consistent with the view that the oxo acid is an intermediate in the formation of ethylene from methionine.