Effects of manganese ions and magnesium ions on the activity of soya-bean ribulose bisphosphate carboxylase/oxygenase

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Abstract
The Michaelis constants of soybean ribulose bisphosphate carboxylase for CO2 in the carboxylation reaction and for O2 in the oxygenation reaction depend on the nature of the bivalent cation present. In the presence of Mg2+ the Km for bicarbonate is 2.48 mM, and the Km for O2 is 37% (gas-phase concentration). With Mn2+ the values decrease to 0.85 mM and 1.7%, respectively. For the carboxylation reaction, Vmax was 1.7 .mu.mol/min per mg of protein with Mg2+ but only 0.29 .mu.mol/min per mg of protein with Mn2+. For the oxygenation reaction, Vmax values were 0.61 and 0.29 .mu.mol/min per mg of protein, respectively, with Mg2+ and Mn2+.