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Seasonal Changes in the Kinetic Parameters of a Photosynthetic Fructose-1,6-Bisphosphatase Isolated from Peltigera rufescens¹

Department of Biology, McMaster University, Hamilton, Ontario, Canada L8S 4K1

The kinetic parameters of the photosynthetic fructose-1,6-bisphosphatase isolated from Peltigera rufescens (Weis) Mudd. were measured on a seasonal basis and during a laboratory-induced temperature acclimation. Both the substrate affinity and Ea changed on a seasonal basis. During the summer, the Ea decreased from 91.8 to 62.3 kilojoules per mole. The K_m fructose-1,6-bisphosphate measured at temperatures above 25°C was also found to decrease by 50%. This seasonal change in K_m can be induced by growing the lichen under appropriate conditions for 2 weeks, and is correlated to a change in the net photosynthetic rates. It is hypothesized that this change in fructose-1,6-bisphosphatase is related to the seasonal temperature acclimation process that has been previously reported in this species.