Recycling of 5′-Methylthioadenosine-Ribose Carbon Atoms into Methionine in Tomato Tissue in Relation to Ethylene Production

Abstract

The ribose moiety of 5′-methylthioadenosine (MTA) is metabolized to form the four-carbon unit (2-aminobutyrate) of methionine in tomato tissue (Lycopersicon esculentum Mill., cv. Pik Red). When [U-¹⁴C-adenosine] MTA was administered to tomato tissue slices, label was recovered in 5-methylthioribose (MTR), methionine, 1-aminocyclopropane-1-carboxylic acid (ACC), C₂H₄ and other unidentified compounds. However, when [U-¹⁴C-ribose]MTR was administered, radioactivities were recovered in methionine, ACC and C₂H₄, but not MTA. This suggests that C₂H₄ formed in tomato pericarp tissue may be derived from the ribose portion of MTA via MTR, methionine and ACC. The conversion of MTR to methionine is not inhibited by aminoethoxyvinylglycine (AVG), but is O₂ dependent. These data present a new salvage pathway for methionine biosynthesis which may be important in relation to polyamine and ethylene biosynthesis in tomato tissue.