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'Alternative Substrate' in keywords Facet   section ZfN Section C  [X]
Facet   Publication Year 1995  [X]
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1Author    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