Methionine Metabolism in Apple Tissue: Implication of S-Adenosylmethionine as an Intermediate in the Conversion of Methionine to Ethylene 1

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RESUMO

If S-adenosylmethionine (SAM) is the direct precursor of ethylene as previously proposed, it is expected that 5′-S-methyl-5′-thioadenosine (MTA) would be the fragment nucleoside. When [Me-14C] or [35S]methionine was fed to climacteric apple (Malus sylvestris Mill) tissue, radioactive 5-S-methyl-5-thioribose (MTR) was identified as the predominant product and MTA as a minor one. When the conversion of methionine into ethylene was inhibited by l-2-amino-4-(2′-aminoethoxy)-trans-3-butenoic acid, the conversion of [35S] or [Me14C]methionine into MTR was similarly inhibited. Furthermore, the formation of MTA and MTR from [35S]methionine was observed only in climacteric tissue which produced ethylene and actively converted methionine to ethylene but not in preclimacteric tissue which did not produce ethylene or convert methionine to ethylene. These observations suggest that the conversion of methionine into MTA and MTR is closely related to ethylene biosynthesis and provide indirect evidence that SAM may be an intermediate in the conversion of methionine to ethylene.

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