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The reductive pentose phosphate cycle for photosynthetic CO 2 assimilation: enzyme modulation
Author(s) -
Wolosiuk Ricardo A.,
Ballicora Miguel A.,
Hagelin Karin
Publication year - 1993
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.7.8.8500687
Subject(s) - biochemistry , ribulose , ferredoxin , rubisco , pentose phosphate pathway , chloroplast , thioredoxin , enzyme , chemistry , thioredoxin reductase , biology , glycolysis , gene
The reductive pentose phosphate cycle (Benson‐Calvin cycle) is the main biochemical pathway for the conversion of atmospheric CO 2 to organic compounds. Two unique systems that link light‐triggered events in thylakoid membranes with enzyme regulation are located in the soluble portion of chloroplasts (stroma): the ferredoxin‐thioredoxin system and ribulose 1,5‐bisphosphate carboxylase/oxygenase‐Activase (Rubisco‐Activase). The ferredoxin‐thioredoxin system (ferre‐doxin, ferredoxin‐thioredoxin reductase, and thioredoxin) transforms native (inactive) glyceraldehyde‐3‐P dehydrogenase, fructose‐1,6‐bisphosphatase, sedoheptulose‐1,7‐bisphosphatase, and phosphoribulokinase to catalytically competent forms. However, the comparison of enzymes reveals the absence of common amino acid sequences for the action of reduced thioredoxin. Thiol/disulfide exchanges appear as the underlying mechanism, but chloroplast metabolites and target domains make the activation process peculiar for each enzyme. On the other hand, Rubisco‐Activase facilitates the combination of CO 2 with a specific ϵ‐amino group of ribulose 1,5‐bisphosphate carboxylase/oxygenase and the subsequent stabilization of the carbamylated enzyme by Mg 2+ , in a reaction that depends on ATP and ribulose 1,5‐bisphosphate. Most of these studies were carried out in homogenous solutions; nevertheless, a growing body of evidence indicates that several enzymes of the cycle associate either with thylakoid membranes or with other proteins yielding supra‐molecular complexes in the chloroplast.—Wolosiuk, R. A.; Ballicora, M. A.; Hagelin, K. The reductive pentose phosphate cycle for photosynthetic CO 2 assimilation: enzyme modulation. FASEB J. 7: 622‐637; 1993.