Isolation of L8 and L8S8 forms of ribulose bisphosphate carboxylase/oxygenase from Chromatium vinosum.

The enzyme ribulose bisphosphate carboxylase/oxygenase has been purified from Chromatium vinosum. When an extract is subjected to centrifugation at 35,000 X g in the presence of polyethylene glycol (PEG)-6000 and the supernatant is treated with 50 mM Mg2+ and the precipitate is then fractionated by vertical centrifugation into a reoriented sucrose gradient followed by chromatography on diethylaminoethyl (DEAE)-Sephadex A50, the resultant enzyme contains large (L) and small (S) subunits. Alternatively, centrifugation of extracts at 175,000 X g in the presence of PEG-6000 followed by fractionation with Mg2+, density gradient centrifugation, and chromatography on DEAE-Sephadex A50 yields an enzyme free of small subunits. The two forms have comparable carboxylase and oxygenase activities and have compositions and molecular weights corresponding to L8 and L8S8 enzymes. The amino acid compositions of L and S subunits are reported. The L8S8 enzyme from spinach cannot be similarly dissociated by centrifugation at 175,000 X g in the presence of PEG-6000.