Coarse Control of Sucrose-Phosphate Synthase
In green plant tissue the photosynthate is transported to the sink regions of the plant as sucrose. In order to investigate plant physiology it is of great interest to look at the regulation of sucrose synthesis. In the reaction sequence leading to sucrose one of the steps that are thought to be regulated is the reaction catalized by sucrose-phosphate synthase in which fructose-6-phosphate and UDP-glucose are converted to sucrose-phosphate and UDP. When people measure sucrose-phosphate synthase activity in spinach leaves at different times of a day they find a diurnal rhythm when the reaction is assayed using conditions that correspond to in vivo concentrations. A diurnal rhythm measured under Vmax conditions, however, results in constant activities over 24 hours. Thus the properties of sucrose-phosphate synthase change during the day: In the morning the enzyme shows high activity that is hardly influenced by physiological phosphate concentrations and in the evening it has low activity that is inhibited by physiological phosphate concentrations, only leaving a residual activity of about 10%. We now wish to characterize these two forms of sucrose-phosphate synthase, whose relative amount change in leaves and produce the diurnal changes. We aim to purify the enzyme so far that kinetic studies can be done.
KeywordsDiurnal Rhythm Diurnal Change Constant Activity Fast Protein Liquid Chromatography Sucrose Synthesis
- Stitt, M., Huber, S., and Kerr, P., (1987), Control of photosynthetic sucrose formation In: The Biochemistry of Plants, Vol. 10, pp. 327–409, Hatch, M.D. and Boardman, N.K., eds.Google Scholar