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Stimulation of Ribulose Bisphosphate Carboxylase Activity by Inorganic Orthophosphate without an Increase in Bound Activating CO2: Co-operativity between the Subunits of the Enzyme

Material type: TextSeries: ; Journal of Experimental Botany, 36(9), p.1396-1404, 1985Contained works:
  • Parry, M.A.J
  • Godfrey Schmidt, C.N
  • Cornelius, M.J
  • Keys, A.J
  • Millard, B.N
  • Gutteridge, S
Subject(s): Online resources: Abstract: Ribulose bisphosphate carboxylase/oxygenase (E.C. 4.1.1.39)from wheat (Triticum aestivum L.), already activated by reaction with CO2 and Mg2+, was increased in activity on addition of inorganic orthophosphate. This further activation took place without a significant increase in the amount of bound activating CO2 and the effect was relatively greater with smaller amounts of bound CO2. With less than 2-0 mol of CO2 bound per mol holoenzyme, phosphate increased activity about five-fold whilst with 70 mol of bound activating CO2 per mol holoenzyme, phosphate increased activity by a factor of only 1 -8. This decrease in the effect of orthophosphate with increase in bound activating CO2 suggests negative co-operativity between activated sites. The stimulation of activity by inorganic orthophosphate must be a process distinct from activation by CO2; it was observed with both the slow and the rapidly activating forms of ribulose bisphosphate carboxylase/oxygenase from wheat.
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Ribulose bisphosphate carboxylase/oxygenase (E.C. 4.1.1.39)from wheat (Triticum aestivum L.), already activated by reaction with CO2 and Mg2+, was increased in activity on addition of inorganic orthophosphate. This further activation took place without a significant increase in the amount of bound activating CO2 and the effect was relatively greater with smaller amounts of bound CO2. With less than 2-0 mol of CO2 bound per mol holoenzyme, phosphate increased activity about five-fold whilst with 70 mol of bound activating CO2 per mol holoenzyme, phosphate increased activity by a factor of only 1 -8. This decrease in the effect of orthophosphate with increase in bound activating CO2 suggests negative co-operativity between activated sites. The stimulation of activity by inorganic orthophosphate must be a process distinct from activation by CO2; it was observed with both the slow and the rapidly activating forms of ribulose bisphosphate carboxylase/oxygenase from wheat.

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