A homolog of ribulose bisphosphate carboxylase/oxygenase-binding protein in Chromatium vinosum.

A 700-kDa protein composed of 12 apparently identical 60-kDa subunits copurifies with the L8S8 form of ribulose bisphosphate carboxylase/oxygenase (RuBisCO) from Chromatium vinosum. Chromatography on DEAE-Sephadex A-50 separates the two proteins in pure form. On the basis of the highly reproducible copurification and reaction of the 700-kDa protein with antibodies to pea RuBisCO large (L)-subunit-binding protein, the protein from C. vinosum is designated as a putative binding protein (PBP) for RuBisCO. Also the N-terminal sequence of PBP is quite similar to that of both alpha and beta subunits of the L-subunit-binding protein. Our present research suggests that PBP may be a RuBisCO small-subunit-binding protein in C. vinosum. Measurements of RuBisCO activity and of species that immunologically cross react with RuBisCO or PBP (by enzyme-linked immunosorbent assay) establish that levels of the two proteins vary together in C. vinosum grown on different carbon sources.