Effects of rare earth ions on activity of RuBPcase in tobacco

To investigate the physiological effects of rare earth ions, we have studied the effect of LaCl3 on the activity of ribulose 1,5-bisphosphate carboxylase (RuBPcase) in tobacco (Nicotiana tobacum). When treated with 20-80 mu mol/l LaCl3 in Hoagland solution by water culture or by spraying with 400-1600 mu mol/l LaC(l)3 in pot experiment, the total and initial activities of RuBPcase were raised gradually, but decreased when the concentrations of LaCl3 were greater than or equal to 200 mu mol/l in water culture and > 1600 mu mol/l by spraying. it was indicated that LaCl3 promoted the activation of RuBPcase at low concentrations in vivo. It was also proved that lanthanides (Ln(3+)) increased the activity of RuBPcase in vitro. Upon addition of different concentrations of Ln(3+) to replace Mg2+, the RuBPcase activity exhibited an apparently biphasic response curve. Among the three Ln(3+) tested, the activation effects of La3+ and Ce3+ on RuBPcase were greater than that of Gd3+, but the activation effects of all the three Ln(3+) were lower at high concentrations than that of Mg2+, showing strongly inhibitory function. The extended X-ray absorption fine structure study of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco)-La complex indicated that La is bound with the oxygen atoms of amino acid residues, with the distance of the La-O bond being 2.51 Angstrom. The mechanism of molecular interaction between Ln(3+) and RuBPcase is discussed. (C) 2000 Published by Elsevier Science Ireland Ltd. All rights reserved.