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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Plant molecular biology 16 (1991), S. 967-974 
    ISSN: 1573-5028
    Keywords: carotenogenesis ; herbicide resistance ; norflurazon ; nicotinamide-adenine-dinucleotide ; phytoene desaturase ; Synechococcus PCC7942
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have cloned and sequenced a gene, pds, from the cyanobacterium Synechococcus PCC7942 that is responsible for resistance to the bleaching herbicide norflurazon. A point mutation in that gene, leading to an amino acid substitution from valine to glycine in its polypeptide product, was found to confer this resistance. Previous studies with herbicide-resistant mutants have indicated that this gene encodes phytoene desaturase (PDS), a key enzyme in the biosynthesis of carotenoids. A short amino acid sequence that is homologous to conserved motifs in the binding sites for NAD(H) and NADP(H) was identified in PDS, suggesting the involvement of these dinucleotides as cofactors in phytoene desaturation.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5079
    Keywords: bicarbonate effect ; cyanobacterium ; D1 protein ; herbicide-resistance ; Photosystem II ; (Synechococcus sp. PCC 7942)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We examined the effects of mutations at amino acid residues S264 and F255 in the D1 protein on the binding affinity of the stimulatory anion bicarbonate and inhibitory anion formate in Photosystem II (PS II) in Synechococcus sp. PCC 7942. Measurements on the rates of oxygen evolution in the wild type and mutant cells in the presence of different concentrations of formate with a fixed bicarbonate concentration and vice versa, analyzed in terms of an equilibrium activator-inhibitor model, led to the conclusion that the equilibrium dissociation constant for bicarbonate is increased in the mutants, while that of the formate remains unchanged (11±0.5 mM). The hierarchy of the equilibrium dissociation constant for bicarbonate (highest to lowest, ±2 μM) was: D1-F255L/S264A (46 μM)〉D1-F255Y/ S264A (31 μM)≈D1-S264A (34 μM)≈D1-F255Y (33 μM)〉wild type (25 μM). The data suggest the importance of D1-S264 and D1-F255 in the bicarbonate binding niche. A possible involvement of bicarbonate and these two residues in the protonation of QB -, the reduced secondary plastoquinone of PS II, in the D1 protein is discussed.
    Type of Medium: Electronic Resource
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