Evidence That the Pathway of Dimethylsulfoniopropionate Biosynthesis Begins in the Cytosol and Ends in the Chloroplast.
AUTOR(ES)
Trossat, C.
RESUMO
In the flowering plant Wollastonia biflora (L.) DC. the first step in 3-dimethylsulfoniopropionate (DMSP) synthesis is conversion of methionine to S-methylmethionine (SMM) and the last is oxidation of 3-dimethylsulfoniopropionaldehyde (DMSP-ald) (F. James, L. Paquet, S.A. Sparace, D.A. Gage, A.D. Hanson [1995] Plant Physiol 108: 1439-1448). DMSP-ald was shown to undergo rapid, spontaneous decomposition to dimethylsulfide and acrolein. However, it was stable enough (half-life [greater than or equal to] 1 h) in tertiary amine buffers to use as a substrate for enzyme assays. A dehydrogenase catalyzing DMSP-ald oxidation was detected in extracts of W. biflora mesophyll protoplasts. This enzyme had a high affinity for DMSP-ald (Km = 1.5 [mu]M), was subject to substrate inhibition, preferred NAD to NADP, and was immunologically related to plant betaine aldehyde dehydrogenases. After fractionation of protoplast lysates, [greater than or equal to]90% of DMSP-ald dehydrogenase activity was recovered from the chloroplast stromal fraction, whereas the enzyme that mediates SMM synthesis, S-adenosylmethionine:methionine S-methyltransferase, was found exclusively in the cytosolic fraction. Immunohistochemical analysis confirmed that the S-methyltransferase was cytosolic. Intact W. biflora chloroplasts were able to metabolize supplied [35S]SMM to [35S]DMSP. These findings indicate that SMM is made in the cytosol, imported into the chloroplast, and there converted successively to DMSP-ald and DMSP.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=160964Documentos Relacionados
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