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1995 (1)
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1Author    Jiro Hoshino, Uta Kühne, Branka Filjak, Hans KrögerRequires cookie*
 Title    Regulation and Characterization of L-Serine: Pyruvate Aminotransferase in Rat Liver Cytosol and Mitochondria  
 Abstract    Distribution of rat liver serine: pyruvate aminotransferase between cytosol and mitochondria varies considerably with the dietary and hormonal state of animals. Feeding a high-protein diet or fasting the animals results in an increase in the enzyme activity of both fractions but more marked in the mitochondrial fraction. A low-protein diet exerts the reverse effect. A single ad­ ministration of dibutyryl cyclic AMP causes a rapid elevation of the enzyme activity in both fractions, which is effectively prevented by cycloheximide, actinomycin D and cortisone. The activity in mitochondria increases with a lag of 2 h following injection of the nucleotide inducer, in contrast to the cytosol enzyme, which increases without any lag. Gel filtration and DEAE cellulose chromatography of the enzyme from both fractions revealed the similar pattern and some kinetic constants of these two types of the enzyme were not significantly different from each other. These results indicate that rat liver serine: pyruvate aminotransferase is synthesized in the extra-mito-chondrial site and transfered to mitochondria. 
  Reference    (Z. Naturforsch. 32c, 249 [1977]; received January 13/February 21 1977) 
  Published    1977 
  Keywords    Serine: Pyruvate Aminotransferase, Cytosol, Mitochondria, Dibutyryl Cyclic Adenosine Monophosphate 
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 TEI-XML for    default:Reihe_C/32/ZNC-1977-32c-0249.pdf 
 Identifier    ZNC-1977-32c-0249 
 Volume    32 
2Author    Ruth Hracky, Jürgen SollRequires cookie*
 Title    Protein Phosphorylation — Dephosphorylation in the Cytosol of Pea Mesophyll Cells  
 Abstract    Soluble protein kinase and protein phosphatase activities were localized in the cytosol of pea mesophyll cells using protoplasts fractionation techniques. The molecular weights of the phos-phorylated cytosolic proteins, as determined by polyacrylamide gel electrophoresis, were 68, 55, 46, 38, 36, 30, 22 and 12 kDa. Histone and, to a much lesser extent, casein but not phosvitin were accepted as exogenous substrates. In every case serine served as acceptor amino acid for the phosphate residue. The protein phosphorylation activity had an alkaline pH optimum, and showed no response to varying Mg2+, Ca2+, Pn cyclo-AMP or calmodulin concentrations. The kinase activity was competitively inhibited by ADP and pyrophosphate with apparent K t values of 0.5 and 0.17 m M , respectively. High ATP concentrations (1 -4 m M) resulted in a strong decrease of radioactivity in the ,2P labeled proteins. It is proposed that the ratio of protein phosphorylation to protein dephosphorylation is regulated by the ATP to ADP ratio in the cytosol. 
  Reference    Z. Naturforsch. 41c, 856 (1986); received July 9/August 5 1986 
  Published    1986 
  Keywords    Protein Kinase, Protein Phosphatase, Cytosol, Protoplasts, Pisum sativum 
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 TEI-XML for    default:Reihe_C/41/ZNC-1986-41c-0856.pdf 
 Identifier    ZNC-1986-41c-0856 
 Volume    41 
3Author    LeszekA. KleczkowskiRequires cookie*
 Title    Kinetics and Regulation of the NAD(P)H-Dependent Glyoxylate-Specific Reductase from Spinach Leaves  
 Abstract    Kinetic mechanism of purified spinach leaf NAD(P)H glyoxylate reductase (GR-1) was studied using either NADPH and NADH as alternative substrates with glyoxylate. The mech­ anism was elucidated from substrate kinetic patterns using NADH as a cofactor rather than NADPH. With NADPH varied versus glyoxylate, and with NADPH and glyoxylate varied at a constant ratio, the patterns obtained on double reciprocal plots appeared to be consistent with a ping-pong mechanism; however, kinetic patterns with NADH conclusively ruled out the ping-pong reaction in favour of the sequential addition of the reactants. Product inhi­ bition studies with glycolate and NADP have suggested either that NADPH binds to the enzyme before glyoxylate or that the addition of substrates is a random one. Studies with active group modifiers suggested an involvement of histidine, serine and cysteine residues in GR-1 activity. Salts had little or no effect on the activity of the enzyme, with the exception of cyanide, which had an apparent K, of ca. 2 m M . Studies with several metabolites used as possible effectors of GR-1 activity have suggested that the enzyme is modulated only by substrate availability in vivo. The apparent insensitivity of GR-1 to metabolic effectors is consistent with the proposed role of the enzyme in detoxifying glyoxylate which may act as a potent inhibitor of photosynthetic processes in plant tissues. 
  Reference    Z. Naturforsch. 50c, 21—28 (1995); received October 21/November 21 1994 
  Published    1995 
  Keywords    Alternative Substrate, Cyanide, Cytosol, Glycolate Pathway, Glyoxylate Reductase 
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 TEI-XML for    default:Reihe_C/50/ZNC-1995-50c-0021.pdf 
 Identifier    ZNC-1995-50c-0021 
 Volume    50