Evidence that the pathway of dimethylsulfoniopropionate biosynthesis begins in the cytosol and ends in the chloroplast

• Published in: Plant physiology (Bethesda) Vol. 111; no. 4; pp. 965 - 973
• Main Authors: Trossat, C. (University of Florida, Gainesville, FL.), Nolte, K.D, Hanson, A.D
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Physiologists 01.08.1996
• Subjects: ACTIVIDAD ENZIMATICA; ACTIVITE ENZYMATIQUE; Aldehydes; Betaines; biochemical pathways; Biochemistry and Enzymology; Biological and medical sciences; BIOSINTESIS; BIOSYNTHESE; Biosynthesis; Chlorophylls; CHLOROPLASTE; Chloroplasts; CITOPLASMA; CLOROPLASTO; COMPOSE AMINE; COMPOSITAE; COMPUESTOS DE AMINA; CYTOPLASME; Cytosol; Dehydrogenases; enzyme activity; Enzymes; Fundamental and applied biological sciences. Psychology; IDENTIFICACION; IDENTIFICATION; kinetics; Metabolism; Metabolism. Physicochemical requirements; oxidoreductases; OXIDORREDUCTASAS; OXYDOREDUCTASE; Plant physiology and development; Plants; PROPIONATE; propionates; PROPIONATOS; Protoplasts; TRANSFERASAS; TRANSFERASE; transferases; VIA BIOQUIMICA DEL METABOLISMO; VOIE BIOCHIMIQUE DU METABOLISME; Wedelia; Cell compartment; Intracellular transport; Biosynthesis; Metabolic pathway; Compositae; Cytosol; Immunological method; Dicotyledones; Angiospermae; Spermatophyta; Biosynthesis precursor; Localization; Sulfonium compound; Chloroplast
• ISSN: 0032-0889; 1532-2548; 1532-2548
• DOI: 10.1104/pp.111.4.965

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 micromolar), 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