The effect of SO 3 -- on the activity of ribulose-1,5-diphosphate carboxylase in isolated spinach chloroplasts

SO 3 -- inhibits the activity of ribulose-1,5-diphosphate carboxylase in isolated spinach chloroplasts. It shows a non-competitive inhibition pattern with respect to ribulose-1,5-diphosphate and Mg++ but a competitive one with respect to HCO 3 - . The K i -values are 14 mM SO 3 -- and 9.5 mM SO 3 - respectively for the non-competitive inhibition but only 3.0 mM SO 3 -- in the case of competitive inhibition with HCO 3 -- as a substrate. Thus it is concluded that the competitive inhibition type will predominate at low SO 3 -- and low internal CO2 concentrations.