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How various factors influence the CO2/O2 specificity of ribulose-1,5-bisphosphate carboxylase/oxygenase

How various factors influence the CO2/O2 specificity of ribulose-1,5-bisphosphate... Temperature, activating metal ions, and amino-acid substitutions are known to influence the CO2/O2 specificity of the chloroplast enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase. However, an understanding of the physical basis for enzyme specificity has been elusive. We have shown that the temperature dependence of CO2/O2 specificity can be attributed to a difference between the free energies of activation for the carboxylation and oxygenation partial reactions. The reaction between the 2,3-enediolate of ribulose 1,5-bisphosphate and O2 has a higher free energy of activation than the corresponding reaction of this substrate with CO2. Thus, oxygenation is more responsive to temperature than carboxylation. We have proposed possible transition-state structures for the carboxylation and oxygenation partial reactions based upon the chemical natures of these two reactions within the active site. Electrostatic forces that stabilize the transition state of the carboxylation reaction will also inevitably stabilize the transition state of the oxygenation reaction, indicating that oxygenase activity may be unavoidable. Furthermore, the reduction in CO2/O2 specificity that is observed when activator Mg2+ is replaced by Mn2+ may be due to Mg2+ being more effective in neutralizing the negative charge of the carboxylation transition state, whereas Mn2+ is a transition-metal ion that can overcome the triplet character of O2 to promote the oxygenation reaction. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Photosynthesis Research Springer Journals

How various factors influence the CO2/O2 specificity of ribulose-1,5-bisphosphate carboxylase/oxygenase

Chen, Zhixiang; Spreitzer, Robert
Photosynthesis Research , Volume 31 (2) – Apr 19, 2004
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References (32)

Publisher
Springer Journals
Copyright
Copyright
Subject
Life Sciences; Plant Sciences; Plant Physiology; Biochemistry, general; Plant Genetics and Genomics
ISSN
0166-8595
eISSN
1573-5079
DOI
10.1007/BF00028792
Publisher site
See Article on Publisher Site

Abstract

Temperature, activating metal ions, and amino-acid substitutions are known to influence the CO2/O2 specificity of the chloroplast enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase. However, an understanding of the physical basis for enzyme specificity has been elusive. We have shown that the temperature dependence of CO2/O2 specificity can be attributed to a difference between the free energies of activation for the carboxylation and oxygenation partial reactions. The reaction between the 2,3-enediolate of ribulose 1,5-bisphosphate and O2 has a higher free energy of activation than the corresponding reaction of this substrate with CO2. Thus, oxygenation is more responsive to temperature than carboxylation. We have proposed possible transition-state structures for the carboxylation and oxygenation partial reactions based upon the chemical natures of these two reactions within the active site. Electrostatic forces that stabilize the transition state of the carboxylation reaction will also inevitably stabilize the transition state of the oxygenation reaction, indicating that oxygenase activity may be unavoidable. Furthermore, the reduction in CO2/O2 specificity that is observed when activator Mg2+ is replaced by Mn2+ may be due to Mg2+ being more effective in neutralizing the negative charge of the carboxylation transition state, whereas Mn2+ is a transition-metal ion that can overcome the triplet character of O2 to promote the oxygenation reaction.

Journal

Photosynthesis Research – Springer Journals

Published: Apr 19, 2004

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