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Title: Properties and synthesis of the ribulose-1,5-biphosphate carboxylase large subunit binding protein
Author: Morgan, Catherine Ruth
ISNI:       0000 0001 3420 443X
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1985
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Previous work ha« shown that newly-synthesised and unassembled large subunits of the photosynthetic CO2-fixing enzyme, ribulose-1,5-bisphosphate carboxylase (E.C., are non-covalently associated with another chloroplast stromal protein, termed the carboxylase large subunit-binding protein. In the present work the large subunit-binding protein of Pisum sativum was shown to be present in stromal extracts both as a monomer of subunit molecular weight 59,000, and as an oligomeric complex with which unassembled large subunits are associated. The oligomeric complex is reversibly dissociated into monomers in the presence of MgATP| dissociation is nearly complete at lOmM MgATP, but concentrations as low as O.ImM MgATP are sufficient to cause some dissociation. The large subunit-binding protein complex and ribulose-1,5-bisphosphate carboxylase were purified from leaves of Pisum sativum and antibodies raised against these proteins were used to examine the photoregulation of accumulation of their subunits. On illumination of etiolated Pisum plants, an Increase in the accumulation of all three subunits is observed. The small subunit of the carboxylase was shown to be the most strongly photoregulated of the three subunits. The abundance of small subunit increased 30-fold on illumination of an etiolated apex for 48 hours, while the same light treatment increased the amount of large subunit by 15-fold. The LBU-binding protein is readily detectable in etiolated plants, with amounts increasing three to four-fold on illumination. No close correlation between the accumulation of large subunit-binding protein and either of the carboxylase subunits was observed. Both the small subunit and the large subunit of the carboxylase were found to be present in etiolated Pisum plants and these subunits are present in the form of the holoenzyme. The holoenzyme present in etiolated plants is catalytically active and possesses a specific activity which is the same as that measured in light-grown plants. These data are discussed with reference to the hypothesis that the large subunit-binding protein is involved in the assembly of the carboxylase from its subunits.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QK Botany ; QP Physiology