New insights into the structure and function of sedoheptulose-1,7-bisphosphatase; an important but neglected Calvin cycle enzyme

The photosynthetic carbon reduction (Calvin) cycle is the primary pathway for carbon fixation and the enzyme sedoheptulose-1,7-bisphosphatase functions in the regenerative phase of this cycle where it catalyses the dephosphorylation of sedoheptulose-1,7-bisphosphate. This enzyme is unique to the Calvin cycle and has no counterpart in non-photosynthetic organisms. The isolation and sequence analysis of an SBPase clone has led to a number of investigations which have yielded interesting and novel information on this enzyme and in this paper the biochemistry and molecular biology of SBPase are reviewed. Some recent exciting developments are also reported, including the analysis of transgenic plants with reduced levels of SBPase which has shown that SBPase is a key regulator of carbon flux and mutagenesis studies which have resulted in the identification of the redox active cysteines responsible for the regulation by light of SBPase catalytic activity.