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'Inhibitors' in keywords Facet   section ZfN Section C  [X]
Facet   Publication Year 1985  [X]
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1Author    A. Trebst, B. D. Epka, S. M. Ridley, A. F. HawkinsRequires cookie*
 Title    Inhibition of Photosynthetic Electron Transport by Halogenated 4-Hydroxy-pyridines  
 Abstract    Herbicidal halogen substituted 4-hydroxypyridines are inhibitors of photosynthetic electron flow in isolated thylakoid membranes by interfering with the acceptor side of photosystem II. Tetrabromo-4-hydroxypyridine, the most active compound found, has a pl50-value of 7.6 in the inhibition of oxygen evolution in both the reduction of an acceptor of photosystem I and an acceptor of photosystem II. The new inhibitors displace both metribuzin and ioxynil from the membrane. The 4-hydroxypyridines, like ioxynil, have unimpaired inhibitor potency in Tris-treated chloroplasts, whereas the DCMU-type family of herbicides does not. It is suggested that 4-hydroxypyridines are complementary to phenol-type inhibitors, and a common essential element is proposed. The 4-hydroxypyridines do not inhibit photosystem I or non-cyclic electron flow through the cytochrome b/f complex. But they do have a second inhibition site in photosynthetic electron transport since they inhibit ferredoxin-catalyzed cyclic electron flow, indicating an antimycin-like property. A comparison of the in vitro potency of the compounds with the in vivo potency shows no correlation. A major herbicidal mode of action of the group is related to the inhibition of carotenoid synthesis, and access to the chloroplast lamellae in vivo for inhibition of electron transport may be restricted. 
  Reference    Z. Naturforsch. 40c, 391—399 (1985); received February 28 1985 
  Published    1985 
  Keywords    Herbicides, Hydroxypyridines, Inhibitors, Photosynthesis 
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 TEI-XML for    default:Reihe_C/40/ZNC-1985-40c-0391.pdf 
 Identifier    ZNC-1985-40c-0391 
 Volume    40 
2Author    Requires cookie*
 Title    Phosphorylation of Coformycin and 2 -Deoxycoformycin, and Substrate and Inhibitor Properties of the Nucleosides and Nucleotides in Several Enzyme Systems  
 Abstract    Under conditions where 2'-deoxycoformycin is enzymatically phosphorylated by wheat shoot phosphotransferase to the 5'-phosphate in 15—20% yield, coformycin is a relatively poor sub­ strate, and is phosphorylated only to the extent of < 5%. However, chemical phosphorylation of coformycin by modifications of the Yoshikawa procedure led to isolation of coformycin-5'-phos­ phate in 20% overall yield. Coformycin-5'-phosphate was characterized by various criteria, including 'H NMR spectro­ scopy. Comparison of the spectrum with that of the parent nucleoside indicated that the nu­ cleotide is predominantly, although not exclusively, in the conformation anti about the glycosidic bond. Like 2'-deoxycoformycin-5'-phosphate, coformycin-5'-phosphate was a feeble substrate of snake venom 5'-nucleotidase, and is hydrolyzed, quantitatively, at only 2% the rate for 5'-AMP. With 5'-AMP analogues as substrate, the 5'-phosphates of both coformycin and deoxycoformycin were poor inhibitors of the enzyme, with K, values > 0.3 mM. The 5'-phosphates of both coformycin and deoxycoformycin do not significantly inhibit adenosine deaminase (K} > 0.2 m M), but are potent inhibitors of adenylate deaminase (Kj < 10"9 m). Neither coformycin nor deoxycoformycin are inhibitors of mammalian purine nucleoside phosphorylase. The stabilities of coformycin, deoxycoformycin, and their 5'-phosphates, have been examined as a function of pH, and nature of the buffer medium. In particular, all exhibit instability in acid and neutral media, but are relatively stable in the vicinity of pH 9. Some biological aspects of the overall results are presented. 
  Reference    Z. Naturforsch. 40c, 710—714 (1985); received March 5/June 3 1985 
  Published    1985 
  Keywords    Coformycin, 2'-Deoxycoformycin, Phosphorylation, 5'-Phosphates, Substrates, Inhibitors 
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 TEI-XML for    default:Reihe_C/40/ZNC-1985-40c-0710.pdf 
 Identifier    ZNC-1985-40c-0710 
 Volume    40