| | 1 | Author
| CherlaP. Murthy, DavidJ. Deeble, Clemens Von Sonntag | Requires cookie* | | | Title
| The Formation of Phosphate End Groups in the Radiolysis of Polynucleotides in Aqueous Solution  | | | | Abstract
| The polynucleotides poly(U), poly(C), poly(A) and poly(G) have been y-irradiated in N20-and N20/02 (4:l)-saturated aqueous solutions. Hydroxyl radicals from the radiolysis of water react with the polynucleotides thereby producing among other lesions strand breaks. Strand break-age is connected with the formation of phosphomonoester end groups. Such end groups have been determined by measuring inorganic phosphate after a three hour incubation at 37 °C with acid or alkaline phosphatase. In the absence of oxygen G(phosphomonoester end groups) (in units of i^mol J' 1) are 0.47 (poly(U)), 0.17 (poly(C)) and < 0.04 (poly(A) and poly(G)). In the case of poly(U) and poly(C) on heating the sample for one hour at 95 °C prior to incubation with phosphatases the above values increased by 0.14 and 0.07 jxmol J" 1 , resp., whereas such treatment of the purine poly-nucleotides still did not produce a measurable yield of phosphomonoester end groups. Comparing these values with G values for strand breakage taken from the literature, about two phospho-monoester end groups are formed per strand break in poly(U) while for poly(C) this ratio is about unity. The purine polynucleotides show very low yields of strand breakage in agreement with the negligible phosphomonoester yields. In the presence of oxygen G(phosphomonoester end groups) are 0.46 (poly(U)), 0.21 (poly(C)), and < 0.04 (poly(A) and poly(G)). On heating, these values increase, most markedly for poly(U) and poly(C). This is possibly linked to the decomposition of unstable hydroperoxides which are formed in high yields in poly(U) and poly(C) (G = 0.7 and 0.19 nmol J resp.). It is known that at least in the case of poly(U), base radicals attack a sugar moiety and are the main precursors of these lesions. G(phosphomonoester end groups) are considerably lower in the case of the purine polynucleotides. Whether this is due to an inability of the base radicals to attack a sugar moiety or has other reasons must remain an open question. | | | |
Reference
| Z. Naturforsch. 43c, 572—576 (1988); received March 14 1988 | | | |
Published
| 1988 | | | |
Keywords
| Polynucleotides, Strand Break, Phosphomonoester End Group, Oxygen Effect | | | |
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| default:Reihe_C/43/ZNC-1988-43c-0572.pdf | | | | Identifier
| ZNC-1988-43c-0572 | | | | Volume
| 43 | |
| 3 | Author
| GünterF. Wildner, PrafullachandraV. Sane, Jürgen Henkel | Requires cookie* | | | Title
| The Activation of Ribulose-l,5-bisphosphate Carboxylase-Oxygenase from Spinach by Oxygen Changes of the Enzyme Conformation during Air-Argon Transitions | | | | Abstract
| The effect of oxygen on ribulose-l,5-bisphosphate carboxylase-oxygenase from spinach was in vestigated. Both activities were deactivated by removal of oxygen and reversibly reactivated by oxygenation of the enzyme solution. The change in enzyme activities was accompanied by confor mational changes as studied by the use of intrinsic and extrinsic fluorescent probes. The analysis of cysteine sulfhydryl groups accessible to 5,5'-dithiobis-(2-nitrobenzoic acid) re vealed that the number of these groups changed with the oxygen concentration. The kinetic of the exposure of eight cysteine residues was similar to the loss of enzyme activities. The modification of these groups with 5,5'-dithiobis-(2-nitrobenzoic acid) caused almost complete loss of both the activities. The enzyme isolated from a photolithotrophic organism, Chromatium vinosum, was not affected by oxygen removal. During air — argon transitions, neither the enzyme conformation nor the num ber of accessible sulfhydryl groups changed. | | | |
Reference
| Z. Naturforsch. 35c, 239—248 (1980); received December 12 1979 | | | |
Published
| 1980 | | | |
Keywords
| Ribulose-l, 5-bisphosphate Carboxylase, Ribulose-l, 5-bisphosphate Oxygenase, Enzyme Confor mation, Oxygen Effect, Photosynthesis | | | |
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| default:Reihe_C/35/ZNC-1980-35c-0239.pdf | | | | Identifier
| ZNC-1980-35c-0239 | | | | Volume
| 35 | |
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