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The tobacco RuBPcase was purified by the method of (NH 4) 2SO 4 precipitation and Sephadex G 200 column chromatography. The effects of Ln 3+ on inhibition of RuBPcase activity were studied. The results show that the v max (maximum velocity) of RuBPcase does not change, but its k m (Michaelis constant) increases with a k i (inhibitor constant) when increasing the concentration of Ln 3+ in enzymatic reaction. It indicates that the inhibitory action of Ln 3+ on tobacco RuBPcase is a model of competitive inhibition with Mg 2+ . The k i of La 3+ , Ce 3+ and Gd 3+ is 26 3, 34 3 and 200 μmol·L -1 , respectively. Their inhibitory action on the RuBPcase is in the order of La 3+ >Ce 3+ Gd 3+ .
The tobacco effect of Ln 3+ on inhibition of RuBPcase activity were studied. The results show that the v max (maximum velocity) of RuBPcase It does not change, but its km (Michaelis constant) increases with aki (inhibitor constant) when increasing the concentration of Ln 3+ in enzymatic reaction. It indicates that the inhibitory action of Ln 3+ on tobacco RuBPcase is a model of competitive inhibition with Mg 2+. The ki of La 3+, Ce 3+ and Gd 3+ is 26 3, 34 3 and 200 μmol·L -1, respectively. Their inhibitory action on the RuBPcase is in the order of La 3+> Ce 3+ Gd 3+.