Inactive forms of wheat ribulose bisphosphate carboxylase. Conversion from the slowly activating into the rapidly activating form.

Wheat ribulose bisphosphate carboxylase can be converted from the slowly activating into the rapidly activating form by heat or effectors in the absence of CO2 and Mg2+. This conversion process had the same energy of activation of 95.6kJ/mol both in the presence and in the absence of effectors, whereas the free-energy change value ranged from +2.5kJ/mol to -3.4kJ/mol depending on the end product involved. Far-u.v. c.d. spectra measured before and after conversion indicated that ribulose bisphosphate carboxylase is an alpha/beta-class protein and that no significant changes in gross conformation occur. Signals in the near-u.v. region suggested that the main change during conversion is re-orientation of aromatic side chains, probably near the active site; a possible site for effector binding is discussed.