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'Photoinhibition' in keywords Facet   section ZfN Section C:Volume 049  [X]
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1994 (1)
1Author    E. B. Racht, A. TrebstRequires cookie*
 Title    Hypothesis on the Control of D 1 Protein Turnover by Nuclear Coded Proteins in Chlamydomonas reinhardtii  
 Abstract    A hypothesis is presented on the events in the degradation of the D 1 protein of photosys­ tem II in the light. It proposes the existence of a nuclear encoded cleavage system that is turning over and which is m odulated by its phosphorylation state. A new experimental ap­ proach is presented in which the D 1 protein degradation under photoinhibitory light is tested in Chlam ydom onas reinhardtii grown under phosphate deficiency and pretreated with cyclo-heximide. Under these conditions the degradation of the D 1 protein is delayed whereas in C hlam y­ dom onas reinhardtii grown in full medium the D 1 protein is rapidly disappearing in high light upon addition o f chloramphenicol (CAP) or lincomycin for inhibiting the resynthesis of the D 1 protein . Cycloheximide (C H I) has little effect on photoinhibition in such control cells. In cells grown, however, for 20 h in phosphate deficiency -such that there is not yet loss of photosynthesis capacity -pretreatment with cycloheximide or canavanine in low light the degradation of the D 1 protein even in 6 h high light is prevented to an appreciable extent. Further addition of CAP or lincomycin has only a small effect. [14C]leucine incorporation was used to show that there is no resynthesis and that the presence of the D 1 protein is due to a delay of degradation. The results are interpreted to show that excess high light which converts the D 1 protein into a potentially, degradable m ode is not sufficient for degradation of the D 1 protein. A cleavage system is needed as well. It is postulated that under phosphate deficiency and pre­ treatment with CHI or canavanine a nuclear coded cleavage system for the D 1 protein is depleted, i.e. the cleavage system for the rapidly turning over D 1 is also turning over. It is shown that under phosphate deficiency an alkaline phosphatase activity in the chloro­ plast and the thylakoid membrane o f Chlam ydom onas reinhardtii is increased. It is proposed that the ratio of kinase/phosphatase converts an active, stable phosphorylated cleavage system into a labile unphosphorylated and turning over state. 
  Reference    Z. Naturforsch. 49c, 439 (1994); received January 31/May 13 1994 
  Published    1994 
  Keywords    Chlamydomonas, D 1 Protein, Photoinhibition, Photosystem II, Phosphate Deficiency 
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 TEI-XML for    default:Reihe_C/49/ZNC-1994-49c-0439.pdf 
 Identifier    ZNC-1994-49c-0439 
 Volume    49