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1991 (1)
1990 (2)
1988 (1)
1Author    DonaldE M Oreland, FrederickT. CorbinRequires cookie*
 Title    Influence of Safeners on the in vivo and in vitro Metabolism of Bentazon and Metolachlor by Grain Sorghum Shoots: a Preliminary Report  
 Abstract    Metabolism of bentazon and m etolachlor by excised shoots and a microsomal fraction iso­ lated from the shoots, of 3-day-old, dark-grown, grain sorghum (Sorghum bicolor cv. Funk G 522 DR) seedlings was studied. The effects of seed treatments, on the subsequent m etabo­ lism of the herbicides, with the safeners naphthalic anhydride, oxabetrinil, and CGA 133205 were compared against surface-sterilization and Captan-treatm ents. Bentazon was aryl hydroxylated in both in vivo and in vitro studies with the hydroxylated derivative undergoing glycosylation only under in vivo conditions. Both shoots and microsomes isolated from shoots of safener-treated seed showed enhanced metabolism of bentazon relative to the controls. In­ hibition by tetcyclacis, a potent inhibitor of plant cytochrome P-450 monooxygenases, in both the in vivo and in vitro studies, and a requirement for N A DPH in the in vitro studies suggested that the formation of hydroxybentazon was mediated by a cytochrome P-450 monooxygenase. Metolachlor was metabolized to polar material and O-desmethylmetolachlor under in vivo conditions. Only the demethylated product was formed in vitro. Shoots isolated from safener-treated seed showed enhanced form ation o f polar com pounds which were assumed to have arisen from conjugation with glutathione. Tetcyclacis did not affect the formation of the polar components. However, the form ation of O-desmethylmetolachlor was depressed in the shoots excised from safener-treated seed under both in vivo and in vitro conditions. Tetcyclacis com ­ pletely prevented form ation of the demethylated metabolite. Hence, formation of this m eta­ bolite is considered to be P-450 mediated. The differential response obtained with the safeners, i.e., stimulation of aryl hydroxylation o f bentazon and depression of metolachlor demethyla-tion, suggests that the reactions are probably catalyzed by different cytochrome P-450 m ono­ oxygenases. 
  Reference    Z. Naturforsch. 46c, 906—914 (1991); received M arch 26 1991 
  Published    1991 
  Keywords    Microsomes, Metolachlor, Bentazon, Cytochrome P-450, Mixed Function Oxidase 
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 TEI-XML for    default:Reihe_C/46/ZNC-1991-46c-0906.pdf 
 Identifier    ZNC-1991-46c-0906 
 Volume    46 
2Author    W. Häberle, H. G. Ruler, Ph Dutkowski, D. Müller-EnochRequires cookie*
 Title    Light-Induced Activation and Synchronization of the Cytochrome P-450 Dependent Monooxygenase System  
 Abstract    The light-induced enhancement o f the 7-ethoxycoumarin-O-deethylase activity was m eas­ ured in a reconstituted system, consisting o f the enzyme P-450pb_b and the N A D P H -cyto-chrome P-450 reductase. The relative increase o f the activity was about 15%. It is shown that the product release process is accelerated by light. The phases o f the catalytic cycle o f 2 x 1012 protein complexes were locked by periodic application o f light pulses (0.1 s duration, 1.32 s repetition time, and 3 9 0 -4 7 0 nm, 0.27 joule/nm ol P-450). More than 80% o f the active recon­ stituted enzyme com plexes (= "molecular machines") worked in phase after a few light pulses. The phase relation continued even after switching o ff the light pulses. The catalytic cycle time was 1.54 s, giving a turnover number o f 39 min-1. The turnover number, as determined from the enzyme activity under optimum conditions, was 39 m in-1. Due to the dissociation constant o f the P-450pb_b:N A D P H -P -450 reductase complexes [3] only 24% o f the proteins were in the active (= working) state under the conditions used. The lifetime o f this complexes is larger than 6 s since more than 4 cycles o f the free running enzyme can be observed. This is the first report, that all catalytic active complexes in the test tube can be synchronized by an external light source, if the right repetition time o f the pulses is chosen, so that all these "molecular machines" work in phase. 
  Reference    Z. Naturforsch. 45c, 273 (1990); received September 14/November 28 1989 
  Published    1990 
  Keywords    Cytochrome P-450, Light-Induced Activation and Synchronization, Catalytic Cycle Time 
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 TEI-XML for    default:Reihe_C/45/ZNC-1990-45c-0273.pdf 
 Identifier    ZNC-1990-45c-0273 
 Volume    45 
3Author    DonaldE. Moreland, FrederickT. Corbin, WilliamP. Novitzky, CarolE. Parker, KennethB. TomerRequires cookie*
 Title    Metabolism of Metolachlor by a Microsomal Fraction Isolated from Grain Sorghum ( Sorghum bicolor) Shoots  
 Abstract    A microsomal fraction isolated from the shoots of 3-to 4-day-old, dark-grown, grain sor­ ghum (Sorghum bicolor cv. Funk G 522 D R) seedlings was characterized. The preparations had a cytochrome P-450 content that varied from approximately 90 to 150 pmol P-450/mg protein with cytochrome P-420 varying from 0 to 3% of the P-450 content. Type I difference spectra were formed with cinnamic acid and metolachlor, and a type II spectrum was formed with tetcyclacis. In short-term assays with [14C]metolachlor as substrate, the preparations produced a single time-dependent product that separated on silica gel TLC plates developed in benzene/ acetone (2:1, v/v). R F values for metolachlor and the metabolite were approximately 0.70 and 0.48, respectively. The microsomal reaction required N A D PH and oxygen, and was inhibited by carbon monoxide, with the inhibition being partially reversed by actinic light. Compounds known to inhibit the activity of cytochrome P-450 monooxygenases (piperonyl butoxide, tet­ cyclacis, and tridiphane) also prevented formation of the metabolite. Identity of the metabolite was confirmed by TLC and positive ion thermospray LC/MS to be 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-hydroxy-l-methylethyl)acetamide. Hence, the reaction catalyzed by the sorghum microsomes involved O-demethylation of the methoxypropyl side chain of meto­ lachlor. 
  Reference    Z. Naturforsch. 45c, 558—564 (1990); received November 9 1989 
  Published    1990 
  Keywords    Microsomes, Metolachlor, Cytochrome P-450, Mixed Function Oxidase, Herbicide Metabolism 
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 TEI-XML for    default:Reihe_C/45/ZNC-1990-45c-0558.pdf 
 Identifier    ZNC-1990-45c-0558 
 Volume    45 
4Author    Maike Petersen, Ulrich Hanns, Seitz, Ernst ReinhardRequires cookie*
 Title    Characterization and Localization of Digitoxin 12 ß-Hydroxylase from Cell Cultures of Digitalis lanata EHRH  
 Abstract    The cytochrome P-450-dependent monooxygenase digitoxin 12ß-hydroxylase from cell cultures of Digitalis lanata needs NADPH and molecular oxygen and hydroxylates cardiac glycosides with the aglycon of digitoxigenin to the corresponding derivatives of the C-series. Other electron donors cannot replace NADPH. The apparent K" m -values are 26 UM for NADPH, 7.1 ^IM for ß-methyldigitoxin and 10 ^IM for digitoxin. The reaction is inhibited by NADP + and cytochrome c in a competitive mode. The optimum temperature was at 20 °C. Low concentrations of Mn 2+ , Mg 2+ , and EDTA were slightly stimulatory, but there was no strict dependence on divalent cations. Digitoxin 12ß-hydroxylase is very stable at room temperature and the reaction proceeds for more than 20 h. After the addition of 15% glycerol, 70% of the original activity can be retained subsequent to freezing at —18 °C. By means of linear sucrose gradient fractionation of cellular membranes the digitoxin 12ß-hydroxylase was found to be located in the endoplasmic reticulum. 
  Reference    Z. Naturforsch. 43c, 199—206 (1988); received December 8 1987 
  Published    1988 
  Keywords    Cardiac Glycosides, Cytochrome P-450, Digitalis lanata, Digitoxin 12ß-Hydroxylase, Endoplas-mic Reticulum 
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 TEI-XML for    default:Reihe_C/43/ZNC-1988-43c-0199.pdf 
 Identifier    ZNC-1988-43c-0199 
 Volume    43