Temperature adaptation of RuBP carboxylase: kinetic properties in marine Antarctic diatoms

Abstract

Colonization of cold waters by unicellular algae, which are ectothermic organisms, is made possible by the evolutionary development of molecular mechanisms which allow photosynthesis at low temperatures. The apparent activation energy ( E a), Michaelis-Menten constant [ K m(RuBP)], V/K m ratios, temperature, and pH optima of d-ribulose 1,5-bisphosphate carboxylase (RuBP carboxylase) were investigated in three species of Antarctic diatoms, Corethron criophilum Castracane, Nitzschia turgiduloïdes (Hasle), N. kerguelensis O'Meara, and in two temperate species, Skeletonema costatum (Greville) Cleve and Phaeodactylum tricornutum Bohlin. The optimum of activity occurred at the same pH (8.0) for the temperate and Antarctic species. E a values corresponding to these species are the same (≈17 kcal·mol −1). We obtained a minimum K m value at a culture temperature of 4.5°C for the Antarctic species and 20°C for the temperate ones. This minimum K m value (60 μM) is of the same order of magnitude as values found in terrestrial plants. These results suggest the occurrence of mechanisms for the maintenance and regulation of RuBP carboxylase activity in Antarctic diatoms at low temperatures.