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1Author    VickiD. Breazeale, BobB. Buchanan, RicardoA. WolosiukRequires cookie*
 Title    Chloroplast Sedoheptulose 1,7-Bisphosphatase: Evidence for Regulation by the Ferredoxin/Thioredoxin System  
 Abstract    1. A substrate-specific sedoheptulose-l,7-bisphosphatase has been found in chloroplasts and separated from its fructose-1,6-bisphosphatase counterpart. Experiments with antibodies indicate that the two enzymes are structurally different. 2. Activity of the sedoheptulose-l,7-bisphosphatase enzyme was dependent on M g i+ and a reductant. The most effective reductant tested was thioredoxin that was reduced either photochemi-cally via ferredoxin with chloroplasts or chemically with dithiothreitol. Dithiothreitol added alone also activated the enzyme, but reduced glutathione or 2-mercaptoethanol did not. The thioredoxin-activated enzyme was deactivated by oxidized glutathione. 3. The results suggest that the new substrate-specific sedoheptulose-l,7-bisphosphatase depends on light for activity and resembles certain other regulatory enzymes of the reductive pentose phos­ phate cycle in its mode of regulation. 
  Reference    Z. Naturforsch. 33c, 521 (1978); received M ay 16 1978 
  Published    1978 
  Keywords    Sed-P2ase, Ferredoxin, Thioredoxin, Enzyme Regulation 
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 TEI-XML for    default:Reihe_C/33/ZNC-1978-33c-0521.pdf 
 Identifier    ZNC-1978-33c-0521 
 Volume    33 
2Author    BenjaminF. Matthews, JackM W IdholmRequires cookie*
 Title    Expression of Aspartokinase, Dihydrodipicolinic Acid Synthase and Homoserine Dehydrogenase During Growth of Carrot Cell Suspension Cultures on Lysine-and Threonine-Supplemented Media  
 Abstract    Reduction in the amounts o f activity o f the first enzyme, aspartokinase (EC and two branch-point enzymes, dihydrodipicolinic acid synthase (EC and homoserine dehydrogen­ ase (EC, located in the pathway for the synthesis o f aspartate-fam ily am ino acids, oc­ curred when cell suspension cultures of Daucus carota L. var. Danvers were grown in media contain­ ing 2 m M threonine or 2 m M lysine, endproducts of the pathway. Activity o f the lysine-sensitive form of aspartokinase was decreased when cells were grown in medium containing lysine and the ac­ tivity of the threonine-sensitive form was decreased when cells were grown in m edium containing threonine. Activity o f the branch-point enzyme leading to threonine synthesis, hom oserine dehy­ drogenase, was decreased up to 70% in specific activity (units/m g protein) and relative activity (units/g fresh weight) when cells were grown in m edia containing lysine or threonine. Threonine had no effect on the relative activity of dihydrodipicolinic acid synthase, but decreased its specific activity. Lysine decreased the relative activity of the synthase by up to 40%, but had little effect on its specific activity. The decreased activities o f the enzymes were apparently not due to binding of the inhibitory amino acids to the enzymes since homogenization of cells in buffer with 2 m M lysi­ ne and threonine did not decrease the m easurable enzyme activities. These and other results pres­ ented suggest that both forms of the aspartokinase activity and homoserine dehydrogenase activi­ ty can be altered by supplementing the growth medium with lysine or threonine. 
  Reference    Z. Naturforsch. 34c, 1177—1185 (1979); received June 18 1979 
  Published    1979 
  Keywords    Daucus carota, Suspension Cultures, Amino Acids, Enzyme Regulation 
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 TEI-XML for    default:Reihe_C/34/ZNC-1979-34c-1177.pdf 
 Identifier    ZNC-1979-34c-1177 
 Volume    34 
3Author    Meinrad Boll3, LutzW D Webera, Juliana Planac, Andreas Stampfl3, H.M Gcoa ReductaseRequires cookie*
 Title    In Vivo and in Vitro Studies on the Regulatory Link between 3-Hydroxy-3- methylglutaryl Coenzyme A Reductase and Cholesterol 7«-Hydroxylase in Rat Liver  
 Abstract    The activities of 3-hydroxy-3-methylglutaryl CoA reductase (HM GCoA reductase; E C, rate-limiting enzyme of cholesterol biosynthesis, and cholesterol 7a-hydroxylase (E C, key enzyme of the neutral bile acid synthesis pathway, were measured in the microsomal fraction of rat liver and in rat liver cells to investigate the coordinate regula­ tion of the two pathways. Both enzyme activities exhibited the same diurnal rhythm and responded in a coordinate fashion to fasting or bile acid-feeding (decrease) and to cholestyramine-feeding (increase). Cholesterol-feeding decreased the activity of HMGCoA reductase, increased that of choles­ terol 7a-hydroxylase, and concomitantly increased free cholesterol in microsomes. In an ex vivo setting using primary hepatocytes from animals fed a high cholesterol diet the activity of HM GCoA reductase was initially low and that of cholesterol 7a-hydroxylase was elevated. Release of cholesterol into the medium with ongoing incubation caused H M GCoA reductase activity to increase, and that of cholesterol 7a-hydroxylase to decline. Incubation of hepatocytes with a cholesterol-containing lipoprotein fraction stimulated the activity of cholesterol 7a-hydroxylase, but left HMGCoA reductase activity unaffected. The results confirm the idea of a joint regulation of the two key enzymes of cholesterol metabolism in response to the levels of substrate and metabolites, and support the notion that with respect to bile acid and cholesterol levels, respectively, regulation of HM GCoA reductase activity may be secondary to that of cholesterol 7a-hydroxylase. The in vitro studies supply evidence that the effects of cholesterol and bile acid excess or deficiency are direct and do not involve accessory changes of hormone levels or mediators. 
  Reference    Z. Naturforsch. 54c, 371 (1999); received January 18/March 3 1999 
  Published    1999 
  Keywords    Cholesterol 7a-Hydroxylase, Enzyme Regulation, Cholesterol, Rat Liver 
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 TEI-XML for    default:Reihe_C/54/ZNC-1999-54c-0371.pdf 
 Identifier    ZNC-1999-54c-0371 
 Volume    54 
4Author    Helga BaumRequires cookie*
 Title    Aurintricarboxylic Acid and Polynucleotides as Novel Inhibitors of Ribonucleotide Reductases  
 Abstract    , R üdiger H ofm ann, M anfred L am m ers, G a b rie le S ch im p ff-W eilan d , and H artm ut F ollm ann Fachbereich Chem ie (Biochem ie) der Philipps-U niversität Marburg, H ans-M eerwein-Straße, Ribonucleoside diphosphate reductases isolated from Escherichia coli, baker's yeast, Ehrlich ascites tumor cells, and a unicellular green alga (Scenedesmus obliquus) are inhibited strongly and uniformly by the polymeric triphenylmethane dye, aurintricarboxylic acid. The m olecule appears to interact simultaneously with the enzyme's various nucleotide and catalytic (iron-organic radical) sites. Oligo-and polyribonucleotides are also inhibitory. T hese reactions serve as m odels o f the probably physiologic regulation o f ribonucleotide reduction exerted by natural inhibitors. Partial characterization o f an inhibitor fraction found in wheat seed em bryo is described. 
  Reference    Z. Naturforsch. 39c, 276—281 (1984); received October 19 1983 
  Published    1984 
  Keywords    Deoxyribonucleotide Synthesis, Enzyme Regulation, Protein-N ucleic Acid Interaction, Wheat Oligonucleotides 
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 TEI-XML for    default:Reihe_C/39/ZNC-1984-39c-0276.pdf 
 Identifier    ZNC-1984-39c-0276 
 Volume    39 
5Author    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 
6Author    Meinrad Bolla, LutzW D W Eberbc, A.Ndreas StampflbRequires cookie*
 Title    The Effect of y-Hexachlorocyclohexane (Lindane) on the Activities of Liver Lipogenic Enzymes and on Serum Lipids in Rats  
 Abstract    The effect of dietary y-hexachlorocyclohexane (lindane) (5 0 -3 5 0 ppm, 0 .1 7 -1 .1 9 |imol/kg chow) on the activity of enzymes of lipogenesis, viz., fatty acid synthase (FAS; EC, citrate cleavage enzyme (CCE; EC, malic enzym e (ME; EC, glucose-6-phos-phate dehydrogenase (G 6 PDH; EC and 6-phosphogluconate dehydrogenase (PGDH; EC, and on serum lipid levels, was investigated in livers of 35-day-old male Wistar rats. Lindane (150 ppm) caused a substantial decline of enzym e activities within the first 24 h of treatment. The decrease was transient, however, and enzyme activities subsequently recov­ ered despite continuation of lindane feeding. The recovery of enzyme activities was compara­ tively fast in the case of ME, G 6 PDH and PG D H , but very slow with FAS and CCE. A ctivities of lipogenic enzymes decrease when animals are starved, and increase much beyond prestarvation levels upon subsequent refeeding. Lindane in the refeeding diet blunted this overshoot of FAS and CCE activities in a dose-dependent manner. In contrast, activities of ME, G 6 PD H and P G D H responded to low dietary lindane concentrations with a substantial stimulation of the increase o f activity, whereas at high lindane concentrations the overshoot was inhibited. According to their responses to lindane exposure, liver lipogenic enzymes could be grouped into 2 categories with FAS and CCE representing one and ME, G 6 PDH and PG D H representing the other group. Polychlorinated biphenyls (PCBs) in the diet caused basically opposite changes of the activities of the lipogenic enzymes. Co-administration o f lindane and PCBs resulted in an apparent cancellation of effects, suggesting that lindane and PCBs affect fatty acid synthesis at opposite points. Levels of the serum triglycerides were increased significantly as a result of lindane feeding, while serum cholesterol and phospholipid levels were only slightly elevated. The increase of serum triglyceride levels that is routinely observed after refeeding o f starved animals was stimulated even more by low concentrations o f lindane in the refeeding diet, but inhibited by high concentrations. 
  Reference    Z. Naturforsch. 50c, 135 (1995); received August 9/September 16 1994 
  Published    1995 
  Keywords    Lipogenic Enzymes, Rat Liver, y-H exachlorocyclohexane (Lindane), Enzyme Regulation, Serum Lipids 
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 TEI-XML for    default:Reihe_C/50/ZNC-1995-50c-0135.pdf 
 Identifier    ZNC-1995-50c-0135 
 Volume    50