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Title: Ribulose-1,5-biphosphate carboxylase-oxygenase and carbon dioxide fixation in the Rhodospirillaceae
Author: Sani, Alhassan
ISNI:       0000 0001 3551 4755
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1985
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A single step purification procedure has been developed for the Isolation of ribulose bisphosphate carboxylase/oxygenase from a number of photosynthetic bacteria. The method Involves centrifugation of the soluble protein extracts on step sucrose gradients. Two different molecular forms of ribulose bisphosphate carboxylase/ oxygenase have been purified and characterised from Rhodopseudomonas blastica. The enzymes both have carboxylase and oxygenase activities. One of the enzymes (designated Form I) structurally resembles the plant enzymes, having eight large and eight small subunits, whereas the other (Form II) is composed of six large subunits and lacks small subunits. Peptide mapping of the isolated large subunits shows that the proteins are quite distinct, and are probably coded for by different genes. The two enzymes show marked differences in kinetic properties. The Form I enzyme exhibits optimal activity at pH 8.0, is inhibited by low concentrations of 6-phosphogluconate and has a high affinity for CO2 (Km CO2 - 40 μm), while the Form II has a pH optimum of 7.4, Is relatively Insensitive to Inhibition by 6-phosphogluconate and has a lower affinity for CO2 (Km CC > 2 - 102 μm). The in vivo regulation of CO2 fixation and synthesis of the Form I and the Form II enzymes in R. blastica has been studied using batch and continuous culture techniques. Evidence suggests that the synthesis of the Form I enzyme is subject to regulation by a repression/derepression mechanism and this is mediated mainly by the CO2 concentration in the growth medium. The Form II enzyme when svnthesised, is present at low levels and is subject to repression/derepression control by either energy or carbon limitations. The differences in the kinetic and regulatory properties suggest that Rhodopseudomonas blastica synthesises two different molecular forms of ribulose bisphosphate carboxylase/oxygenase as a means of physiological adaptation to variations in the levels of CO2 in its growth environment.
Supervisor: Not available Sponsor: University of Ilorin ; Overseas Research Scholarship
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry ; QP Physiology ; QR Microbiology