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2001 (1)
1Author    N. Orbert, G. Rotjohann3, Yi Huangb, Wolfgang Kowallik3, W. Kowallik@, Biologie Uni-Bielefeld, Norbert De, U. Grotjohann@biologie, Ni-Bielefeld, DeRequires cookie*
 Title    Tricarboxylic Acid Cycle Enzymes of the Ectomycorrhizal Basidiomycete, S u ill us bovinus  
 Abstract    In crude cell extracts o f the ectomycorrhizal fungus, Suillus bovinus, activities o f citrate synthase, aconitase, isocitrate dehydrogenase, succinate dehydrogenase, fumarase, and malate dehydrogenase have been proved and analyzed. Citrate synthase exhibited high affinities for both its substrates: oxaloacetate (K m = 0.018 m M) and acetyl-CoA (K m = 0.014 m M) . A con i­ tase showed better affinity for isocitrate (K m = 0.62 m M) than for citrate (K m = 3.20 m M) . Analysis of isocitrate dehydrogenase revealed only small maximum activity (60 nmol x mg protein-1 x m in-1), the enzyme being exclusively N A D P +-dependent. Using the artificial electron acceptor dichlorophenol indophenol, activity and substrate affinity of succinate d e­ hydrogenase were rather poor. Fumarase proved Fe2+-independent. Its affinity for malate was found higher (K m = 1.19 m M) than that for fumarate (K m = 2.09 m M) . High total activity of malate dehydrogenase could be separated by native PAGE into a slowly running species of (mainly) cytosolic (about 80%) and a faster running species of (mainly) mitochondrial origin. A ffinities for oxaloacetate of the two enzyme species were found identical within limits of significance (K m = 0.24 m M and 0.22 m M) . The assumed cytosolic enzyme exhibited affinity for malate (K m = 5.77 mM) more than one order of magnitude lower than that for oxaloacetate. FPLC on superose 12 revealed only one activity band at a molecular mass of 100 ± 15 kDa. Activities o f 2-oxoglutarate dehydrogenase and of succinyl-CoA synthetase could not be found. Technical problems in their detection, but also existence of an incom plete tricarboxylic acid cycle are considered. Metabolite affinities, maximum activities and pH-dependences of fumarase and of malate dehydrogenase allow the assumption of a reductive instead of oxidative function o f these enzymes in vivo. 
  Reference    Z. Naturforsch. 56c, 334 (2001); received December 13 2000/January 26 2001 
  Published    2001 
  Keywords    Suillus bovinus, Carbohydrate M etabolism, Tricarboxylic Acid Cycle Enzymes 
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 TEI-XML for    default:Reihe_C/56/ZNC-2001-56c-0334.pdf 
 Identifier    ZNC-2001-56c-0334 
 Volume    56