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1Author    Amelia Thereza, Roberto Soares3, Ricardo Dias Lins3, RichardG. Longo3, Ricardo Arrattb, Ferreira3Requires cookie*
 Title    Plural Origins of Molecular Homochirality in Our Biota Part II. The Relative Stabilities of Homochiral and Mixed Oligoribotides and Peptides  
 Abstract    By computer simulations -molecular mechanics and molecular dynamics with the amber force field (Weiner et al., (1986), J. Comp. Chem. 7, 2 3 0 -2 5 2) -we have determined the stabilities of oligoribotide strands built with d -and L-riboses, and of peptide chains with d -and L-amino acid residues. In particular, complementary double-chains of oligoribotides were studied, since they are an important feature of the growing mechanism o f modern nucleic acids. Peptide chains on the other hand, grow without need of a template. We found that mixed oligoribotides are less stable than homochiral ones, and that this chiral effect is less noticeable in peptide chains. The results support the interpretation that L-riboses act as termi­ nators to the template-assisted growth of oligo-r-GD (enantiomeric cross-inhibition; Joyce et al., (1987), Proc. Natl. Acad. Sei. U S A 84, 4 398-4402). Based on this effect, a chemical pathway is proposed which could, under assumed prebiotic conditions, bypass the hindrance of homochiral growth. 
  Reference    Z. Naturforsch. 52c, 89 (1997); received July 10/September 4 1996 
  Published    1997 
  Keywords    Chirality, Peptides, Oligoribotides, Computer Simulations 
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 TEI-XML for    default:Reihe_C/52/ZNC-1997-52c-0089.pdf 
 Identifier    ZNC-1997-52c-0089 
 Volume    52 
2Author    Christian Holzapfel, Robert BauerRequires cookie*
 Title    Computer Simulation of Primary Photosynthetic Reactions — Compared with Experimental Results on 0 2-Exchange and Chlorophyll Fluorescence of Green Plants  
 Abstract    A computer model describing the "Z-scheme" of photosynthetic electron transport in terms of reduction and oxydation of coupled redox pools was built up. Starting from a certain initial state corresponding to the dark adapted state of the photosynthetic system the reduction and reoxidation levels of the pools were calculated during adaptation of the system to a steady state in the light. The changes of calculated redox levels were compared with experimental results of fluorescence and oxygen evolution induction curves. It is shown that the transients in prompt fluorescence and oxygen evolution can be described by reduction and reoxidation of the primary electron acceptor pool and the electron donor pool of photosystem II due to reduction and oxidation of the other pools during adaptation to light. The first depression D in the fluorescence induction curve is explained by the existence of a redox pool X between the primary electron acceptor pool Q of photosystem II and plastoquinone. It is shown that DCMU blocks the electron flow between Q and X. Furthermore, it is shown that the inhibitor DBMIB probably not only blocks the electron flow but also causes a successive disconnection of the plastoquinone pool from the electron transport chain. 
  Reference    (Z. Naturforsch. 30c, 489—498 [1975]; received March 3/April 18 1975) 
  Published    1975 
  Keywords    Primary Photosynthetic Electron Transport, Computer Simulation, Fluorescence Induction, Oxygen Exchange Transient 
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 TEI-XML for    default:Reihe_C/30/ZNC-1975-30c-0489.pdf 
 Identifier    ZNC-1975-30c-0489 
 Volume    30 
3Author    Christoph GierschRequires cookie*
 Title    A Kinetic Model for Translocators in the Chloroplast Envelope as an Element of Computersimulation of the Dark Reaction of Photosynthesis  
 Abstract    A kinetic model for the chloroplast translocators (mediating equal and opposite exchange fluxes between the external medium and the stroma) is derived. This model is a modification of the clas­ sical Widdas model corresponding to the exchange of an arbitrary number of compounds with no contribution to net transport. It describes the rate of transport of each compound in simple terms and with a minimum number of kinetic constants. Predictions from the model agree with ex­ perimental data as recorded in the literature. From the experimental apparent kinetic constants FmaX and K m those in terms of the model are calculated. These constants complete the model and make it applicable to the study of metabo­ lism of photosynthesis by means of computer simulation. The set of differential equations describing the operation of the phosphate translocator is solved numerically for some illustrative examples. 
  Reference    (Z. Naturforsch. 32c, 263 [1977]; received November 22 1976) 
  Published    1977 
  Keywords    Chloroplast, Phosphate Translocator, Computer Simulation, Metabolite Exchange, Kinetic Model 
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 TEI-XML for    default:Reihe_C/32/ZNC-1977-32c-0263.pdf 
 Identifier    ZNC-1977-32c-0263 
 Volume    32 
4Author    Christian HolzapfelRequires cookie*
 Title    Analysis of the Prompt Fluorescence Induction by Means of Computer Simulation of the Primary Photosynthetic Reactions  
 Abstract    The induction phenomenon of prompt fluorescence of the photosynthetic system in green plants reflects the adaptation of the electron transport system from a dark adapted state to a steady state under light condition. The appearance of the P-peak in the prompt fluorescence induction curve is explained by the decay of the electrochemical gradient across the thylakoid membrane in the dark. The decay of the electrochemical gradient in the dark is calculated using measured fluorescence induction curves with different times of dark adaptation. The influence of photophosphorylation inhibitors is discussed and the threshold effect of ATP-formation depending on the electrochemical gradient is explained by the coupling of the ATP-formation with the electron transport in the thylakoid membrane. 
  Reference    Z. Naturforsch. 33c, 402—2 (1978); received April 17 1978 
  Published    1978 
  Keywords    Primary Photosynthetic Electron Transport, Computer Simulation, Fluorescence Induction, ATP-Formation 
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 TEI-XML for    default:Reihe_C/33/ZNC-1978-33c-0402.pdf 
 Identifier    ZNC-1978-33c-0402 
 Volume    33