The effect of magnesium and other ions on the distribution of ribulose 1,5-bisphosphate carboxylase in chloroplast extracts |
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Authors: | P.H. McNeil D.A. Walker |
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Affiliation: | ARC Research Group on Photosynthesis, Department of Botany, University of Sheffield, Sheffield S10 2TN, United Kingdom |
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Abstract: | In an attempt to produce chloroplast extracts containing ribulose 1,5-bisphosphate (RuBP) carboxylase in its fully activated state, MgCl2 and NaHCO3 were included in the medium used to osmotically shock chloroplasts. Extracts prepared in this manner contained lower levels of the enzyme than those prepared in the absence of MgCl2 and NaHCO3. The difference in enzyme levels was found to be attributable to an association in the presence of Mg2+, between RuBP carboxylase and the thylakoids removed from the extract during its preparation. Some monovalent cations caused a similar association, although to a lesser extent. The trivalent cation Tris(ethylenediamine) cobalt(III) was more effective in causing this association, but was highly inhibitory to the enzyme. The results suggest that the attraction between thylakoids and RuBP carboxylase in the presence of certain ions is likely to be electrical in nature. The results are discussed in terms of the media used to isolate RuBP carboxylase. |
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