Temperature Dependent Conformation Changes of Ribulose-1,5-bisphosphate Carboxylase Studied by the Use of 1-Anilino-8-naphthalene Sulfonate

Abstract

The influence of temperature on the structure and enzyme activity of ribulose-1,5-bisphosphate carboxylase, isolated from Euglena gracilis cells, was studied. Freezing of the purified ribulose-1,5-bisphosphate carboxylase preparation causes a severe loss of enzyme activity, which can be restored again by incubation of the enzyme molecules at higher temperatures (50 °C). The titration of both enzyme samples with the fluorescence probe 1-anilino-8-naphthalene sulfonate (ANS) re­vealed an increase of the fluorescence emission of the low temperature form of the enzyme. Two different enzyme conformations can be assumed which differ in the number of binding sites for ANS and V_max values for the carboxylase reaction but show similar binding constants for ANS and the apparent K_m values for C0₂ .