Methionine catabolism in Arabidopsis cells is initiated by a gamma-cleavage process and leads to S-methylcysteine and isoleucine synthesis
Résumé
Despite recent progress in elucidating the regulation of methionine synthesis, little is known about the catabolism of this amino acid in plants. We present here several lines of evidence indicating that the cleavage of methionine catalyzed by methionine gamma-lyase is the first step in this process. We have cloned an Arabidopsis cDNA coding a functional methionine gamma-lyase, an enzyme catalyzing the γ-cleavage of methionine into methanethiol, α-ketobutyrate and ammonia. The metabolic role of this enzyme was analyzed in Arabidopsis cells using [13C]-Met and nuclear magnetic resonance (NMR). Beside the accumulation of methionine, adenosylmethionine, and S-methylmethionine, we also identified unequivocally two major metabolites deriving from the catabolism of methionine, namely S-methylcysteine and isoleucine. These data indicate that methionine catabolism in Arabidopsis cells is initiated by a gamma-cleavage process and can result in the formation of the essential amino acid isoleucine and a potential storage form for sulfide or methyl groups, S-methylcysteine.
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