Studies on a conformational change of tobacco ribulose diphosphate carboxylase induced by D-ribulose-1,5-diphosphate

In the presence of d-ribulose diphosphate, crystalline ribulose diphosphate carboxylase from Nicotiana tabacum leaves undergoes a profound change in solubility. The solubility change did not involve a Conformational change in molecular volume exceeding 2% as measured by sedimentation velocity suggesting no gross change in quaternary structure. However, the change in solubility did involve a tertiary structural change wherein some previously buried tyrosyl and tryptophyl residues became exposed, as indicated by difference spectrophotometry. Although the enzyme molecule has 8 binding sites for ribulose diphosphate, the Conformational change is complete after 4 substrate molecules are bound. A cooperative action among the subunits is proposed.