Sucrose synthase isoforms in cultured tobacco cells. |
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| Authors: | Sandra Matic Hans-Erik Akerlund Einar Everitt Susanne Widell |
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| Affiliation: | 1. Department of Cell and Organism Biology, Lund University, Sölvegatan 35B, 22362 Lund, Sweden;2. Department of Plant Biochemistry, P.O. Box 124, 22100 Lund, Sweden;1. Department of Biological Sciences, Vanderbilt University, Nashville, TN, USA;2. Department of Biology, Belmont University, Nashville, TN, USA;1. Instituto de Agrobiotecnología (CSIC/UPNA/Gobierno de Navarra), Iruñako etorbidea 123, 31192 Mutiloabeti, Nafarroa, Spain;2. Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-CSIC, Avenida Américo Vespucio 49, Isla de la Cartuja, 41092 Sevilla, Spain;1. Biological Science and Technology College, Shenyang Agricultural University, Shenyang 110866, P.R. China;2. Key Laboratory of Protected Horticulture, Ministry of Education/College of Horticulture, Shenyang Agricultural University, Shenyang 110866, P.R. China;1. School of Agriculture and Food Science, Zhejiang Agricultural & Forestry University, Wusu Street # 666, Lin’an District, Hangzhou, Zhejiang, 311300, People’s Republic of China;2. School of Environmental and Life Sciences, University of Newcastle, Ourimbah, NSW, 2258, Australia |
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| Abstract: | The plant enzyme sucrose synthase (SuSy; EC 2.4.1.13) catalyzes the reversible conversion of sucrose and UDP into UDP-glucose (UDP-Glc) and fructose. The enzyme exists in different isoforms and is both located in the cytosol, membrane-bound and associated to the actin cytoskeleton. We here investigate sucrose synthase from tobacco (Nicotiana tabacum L.) BY-2 heterotrophic cell suspensions. Two different isoforms of sucrose synthase SuSy1 and SuSy2, could be purified from cytosolic extracts of these cells using a combination of poly(ethylene glycol) (PEG) precipitation, gel filtration, ion-exchange chromatography and affinity chromatography. They were clearly distinct, both with regard to the binding to the ion-exchange column and with regard to their kinetic and regulatory properties. SuSy1, the more abundant species, showed lower V(max) and K(m) for sucrose and UDP compared to the less abundant SuSy2. The activity of SuSy2 in the breakdown direction was stimulated by 60% by actin, in contrast to that of SuSy1, which showed a 17% inhibition. An indication of interaction between SuSy1 and actin was obtained by partitioning in aqueous Dextran-PEG two-phase systems. Furthermore, fructose 2,6-bisphosphate (F26BP) at micromolar concentrations stimulated SuSy2 in the presence of actin while SuSy1 was strongly inhibited by fructose. Possible roles of these two isoforms in the sucrose turnover in BY-2 cells are discussed. |
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