Effects of sulfanilamide and methotrexate on 13C fluxes through the glycine decarboxylase/serine hydroxymethyltransferase enzyme system in Arabidopsis

• Published in: Plant physiology (Bethesda) Vol. 116; no. 1; pp. 137 - 144
• Main Authors: Prabhu, V, Chatson, K.B, Lui, H, Abrams, G.D, King, J
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Physiologists 01-01-1998
• Subjects: ACTIVIDAD ENZIMATICA; ACTIVITE ENZYMATIQUE; Agronomy. Soil science and plant productions; Amino Acid Oxidoreductases - metabolism; Amino acids; AMINOPTERIN; Aminopterin - pharmacology; ANTIMETABOLITE; ANTIMETABOLITES; ANTIMETABOLITOS; ANTIVITAMINAS; ANTIVITAMINE; ANTIVITAMINS; Arabidopsis - enzymology; ARABIDOPSIS THALIANA; BIOCHEMICAL PATHWAYS; Biochemistry and Enzymology; Biological and medical sciences; CARBON; Carbon Isotopes; CARBONE; CARBONO; CARBOXY-LYASES; Cellular metabolism; CHEMICAL REACTIONS; Economic plant physiology; ENZYME INHIBITORS; Enzyme Inhibitors - pharmacology; Enzymes; ENZYMIC ACTIVITY; Fundamental and applied biological sciences. Psychology; GLICINA; GLYCINE (ACIDE AMINE); GLYCINE (AMINO ACID); Glycine - metabolism; Glycine Dehydrogenase (Decarboxylating); Glycine Hydroxymethyltransferase - metabolism; INHIBIDORES DE ENZIMAS; INHIBITEUR D'ENZYME; ION; ION TRANSPORT; IONES; IONS; ISOTOPE RADIOACTIF; Kinetics; LIASAS; LYASE; LYASES; Magnetic Resonance Spectroscopy; Metabolism; Methotrexate - pharmacology; Mitochondria; Multienzyme Complexes - metabolism; Net assimilation, photosynthesis, carbon metabolism. Photorespiration, respiration, fermentation (anoxia, hypoxia); Nuclear magnetic resonance; Nutrition. Photosynthesis. Respiration. Metabolism; Photosynthesis, respiration. Anabolism, catabolism; Plant physiology and development; Plants; Protein metabolism; RADIOACTIVE TRACERS; RADIOISOTOPES; RADIOISOTOPOS; REACCIONES QUIMICAS; REACTION CHIMIQUE; REGULATION; RESPIRACION; RESPIRATION; SERINA; SERINE; Sulfadiazine - pharmacology; SULFAMIDE; Sulfanilamide; Sulfanilamides; Sulfanilamides - pharmacology; SULFONAMIDAS; Sulfonamides; SULPHONAMIDES; Tetrahydrofolates - biosynthesis; TRANSFERASAS; TRANSFERASE; TRANSFERASES; VIA BIOQUIMICA DEL METABOLISMO; VOIE BIOCHIMIQUE DU METABOLISME; Glycine hydroxymethyltransferase; Enzyme; Transferases; Metabolic pathway; Metabolic inhibitor; Glycine; Metabolism; Carbon balance; Sulfanilamide; Arabidopsis thaliana; Regulation(control); Cruciferae; Dicotyledones; Angiospermae; Spermatophyta; Oxidoreductases; Dihydrofolate reductase; Experimental plant; Glycine dehydrogenase (decarboxylating); Methotrexate
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.116.1.137

In C3 plants large amounts of photorespiratory glycine (Gly) are converted to serine by the tetrahydrofolate (THF)-dependent activities of the Gly decarboxylase complex (GDC) and serine hydroxymethyltransferase (SHMT). Using 13C nuclear magnetic resonance, we monitored the flux of carbon through the GDC/SHMT enzyme system in Arabidopsis thaliana (L.) Heynh. Columbia exposed to inhibitors of THF-synthesizing enzymes. Plants exposed for 96 h to sulfanilamide, a dihydropteroate synthase inhibitor, showed little reduction in flux through GDC/SHMT. Two other sulfonamide analogs were tested with similar results, although all three analogs competitively inhibited the partially purified enzyme. However, methotrexate or aminopterin, which are confirmed inhibitors of Arabidopsis dihydrofolate reductase, decreased the flux through the GDC/SHMT system by 60% after 48 h and by 100% in 96 h. The uptake of [alpha-13C]Gly was not inhibited by either drug class. The specificity of methotrexate action was shown by the ability of 5-formyl-THF to restore flux through the GDC/SHMT pathway in methotrexate-inhibited plants. The experiments with sulfonamides strongly suggest that the mitochondrial THF pool has a long half-life. The studies with methotrexate support the additional, critical role of dihydrofolate reductase in recycling THF oxidized in thymidylate synthesis