Ribulose bisphosphate carboxylase from Thiobacillus A2. Its purification and properties |
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Authors: | A M Charles B White |
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Institution: | (1) Department of Biology, University of Waterloo, N2L 3G1 Waterloo, Ontario, Canada |
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Abstract: | Ribulose bisphosphate carboxylase (EC 4.1.1.39) from Thiobacillus A2 has been purified to homogeneity on the basis of polyacrylamide gel electrophoresis and U.V. analysis during sedimentation velocity studies. The enzyme had an optimum pH of about 8.2 with Tris-HCl buffers. The molecular weight was about 521000 with an S
rel. of 16.9. K
m for RuBP was 122 M, for total CO2 it was 4.17 mM, and for Mg2+ 20.0 M. The absolute requirement for a divalent cation was satisfied by Mg2+ which was replaceable to a certain extent by Mn2+. Activity was not significantly affected by SO
4
2-
, SO
3
2-
, or S2O
3
2-
at 1.0 mM. At this concentration S2- caused a 27% stimulation. All mercurials tested were inhibitory. pHMB was the most potent causing about 60% inhibition at 0.01 mM. This inhibition was reversible by low concentrations of cysteine. Cyanide was also inhibitory. Its mode of inhibition with respect to RuBP was un-competitive and with a K
i of 20 M. Lost activity could be restored partially by GSH or Cu2+. Although azide at the concentration tested had no significant effect on enzyme activity, 2,4-dinitrophenol at 1.0 mM caused 91% inhibition. Finally, activity was also affected by energy charge.Abbreviations ATP
adenosine-5 -triphosphate
- GAPDH
glyceraldehyde phosphate dehydrogenase
- GSH
(reduced) glutathione
- G6P
glucose-6-phosphate
- NAD+
nicotinamide adenine dinucleotide
- NADP+
nicotinamide adenine dinucleotide phosphate
- pHMB
parahydroxymercuribenzoate
- 6PG
6-phosphogluconate
- 3-PGA
3-phosphoglycerate
- PGK
phosphoglyceratekinase
- RuBP
ribulose-1,5-bisphosphate |
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Keywords: | Enzymology CO2 fixation Thiobacilli Ribulose bisphosphate carboxylase Regulation Chemolithotrophy |
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