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2001 (1)
1991 (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 
2Author    Abteilung Zellchemie, G.S FRequires cookie*
 Title    Activities and Regulation of Enzymes of Carbohydrate Metabolism in Spruce ( Picea abies) M einrad Boll  
 Abstract    Activities o f the glycolytic enzymes were determined in seedlings, callus cultures and cell sus­ pension cultures o f spruce (Picea abies) (L.) (Karst). The rate-limiting enzymes o f the pathway were the hexokinases, ATP: phosphofructo-kinase, fructose-1,6-bisphosphatase and pyruvate kinase. Two phosphofructokinases were found: A T P : fructose-6-phosphate 1-phosphotransferase (PFK) and pyrophosphate :fructose-6-phosphate 1-phosphotransferase (PFP). In the presence o f its activator fructose-2,6-bisphos-phate, PFP had a 4 -5-fold higher specific activity than PFK. PFP could be activated about 20-fold by fructose-2,6-bisphosphate at saturating concentrations o f the substrates (fructose-6-phosphate and pyrophosphate). The increase o f Fmax was accompanied by a strong increase in the apparent affinity o f the enzyme for the substrates. Km for fructose-6-phosphate and pyrophosphate was 0.44 mM and 24 fiM, respectively. Ka for fructose-2,6-bisphosphate was 24 nM. In seedlings, specific activity o f the glycolytic enzymes was 3 0 -3 0 0 percent higher in the hypocotyls, except for fructose-1,6-bisphosphate aldolase, glyceraldehyde-3-phosphate de­ hydrogenase and phosphoglycerate kinase, their activity being 1 0 0 -150 percent higher in the cotyledons, This distribution remained unchanged during periods o f 2 -16 weeks o f cultiva­ tion o f the seedlings. In callus cultures and in cell suspension cultures, grown mixotrophically with different car­ bohydrates, all enzymes were between 1-and 7-fold higher than in autotrophically grown seed­ lings. Incubation o f seedlings in mineral salt mixture containing a carbohydrate resulted in a rapid coordinate increase o f the activities to the levels o f callus-or cell suspension cultures. This induction required a carbohydrate and oxygen. During prolonged cultivation o f cell sus­ pension cultures, when carbohydrate became limiting, activity o f the enzymes slowly declined. 
  Reference    Z. Naturforsch. 46c, 597 (1991); received Dezember 7 1990/April 4 1991 
  Published    1991 
  Keywords    Picea abies, Cell Culture, Carbohydrate M etabolism, PP, -phosphofructokinase, Enzyme Regulation 
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 TEI-XML for    default:Reihe_C/46/ZNC-1991-46c-0597.pdf 
 Identifier    ZNC-1991-46c-0597 
 Volume    46