d-Ribulose 1,5-diphosphate carboxylase from the blue-green alga Aphanocapsa 6308 |
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Authors: | G A Codd W D P Stewart |
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Institution: | (1) Department of Biological Sciences, University of Dundee, DD1 4HN Dundee, UK |
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Abstract: | d-Ribulose 1,5-diphosphate carboxylase from extracts of the unicellular blue-green alga Aphanocapsa 6308 has been purified by ammonium sulphate precipitation and linear sucrose density gradient centrifugation. The molecular weight was estimated to be 525 000 and the enzyme consisted of two types of sub-unit of molecular weights 51 000 and 15 000. The small sub-units were not detected after purification involving acid precipitation but were observed if the acid precipitation step was omitted. The Michaelis constants for Mg2+ and CO2, when tested under air, were 0.35 mM and 0.071 mM respectively. Oxygen acted as a competitive inhibitor with respect to CO2, suggesting that the enzyme also acts as an oxygenase. This was confirmed by measuring ribulose diphosphate-dependent O2 uptake. A 1:1 stoichiometry between ribulose diphosphate utilization and O2 consumption was observed. 6-Phosphogluconate inhibited carboxylase activity both at high (20 mM) and low (1 mM) bicarbonate concentrations. The data are compared with the properties of ribulose diphosphate carboxylase from other autotrophic prokaryotes and from chloroplasts.Abbreviations RuDP
d-Ribulose 1,5-diphosphate
- EDTA
ethylene diamine tetraacetic acid
- GSH
reduced glutathione
- SDS
sodium dodecyl sulphate
- 6PGluc
6-phosphogluconate
- STB
supplemented Tris buffer |
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Keywords: | d-Ribulose 1 5-diphosphate carboxylase Quaternary structure Oxygenase activity Aphanocapsa |
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