Sani, Alhassan (1985) Ribulose-1.5-bisphosphate carboxylase-oxygenase and carbon dioxide fixation in the 'rhodospirillaceae'. PhD thesis, University of Warwick.

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Abstract

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.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QD Chemistry Q Science > QP Physiology Q Science > QR Microbiology
Library of Congress Subject Headings (LCSH):	Oxygenases, Carbon dioxide, Photosynthetic bacteria, Rhodopseudomonas, Carboxylic acids
Official Date:	July 1985
Dates:	Date Event July 1985 Submitted
Institution:	University of Warwick
Theses Department:	Department of Biological Sciences
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Dow, Crawford S.
Sponsors:	University of Ilorin ; Overseas Research Scholarship
Extent:	xx, 256 leaves : illustrations
Language:	eng

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