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 f or carbon fixation and the enzyme sedoheptulose-1,7-bisphosphatase function s in the regenerative phase of this cycle where it catalyses the dephosphor ylation of sedoheptulose-1,7-bisphosphate. This enzyme is unique to the Cal vin cycle and has no counterpart in non-photosynthetic organisms. The isola tion and sequence analysis of an SBPase clone has led to a number of invest igations which have yielded interesting and novel information on this enzym e and in this paper the biochemistry and molecular biology of SBPase are re viewed. 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 whic h have resulted in the identification of the redox active cysteines respons ible for the regulation by light of SBPase catalytic activity.