Ribulose bisphosphate carboxylases from Chromatium vinosum and Rhodospirillum rubrum and their role in photosynthetic carbon assimilation.

Abstract

Ribulose bisphosphate (RuBP) carboxylase is widely distributed in both prokaryotic (Bacteriophyta and Cyanophyta) and eukaryotic photoautotrophs (Euglenophyta, and Chlorophyta such as Chlorophytina and Tracheophytina). It is also present in some chemosynthetic bacteria. RuBP carboxylase from higher plants and green algae has a molecular weight of (5 to 5.5) × 105 and contains two types of subunits, A (MW 5.5 × 104) and B (MW 1.2 × 104). On the basis of biochemical and immunochemical experiments, it is now well established that the large subunit moiety (A) of the enzyme molecule carries the catalytic site, whereas the small subunit (B) is probably involved in the regulatory function, discussed below. Although the spinach enzyme has been used in the most thorough investigations, in various laboratories, of the structure and function of the carboxylase molecule, other biochemical and biophysical studies have supported the idea that the plant-type enzyme molecule in general has a symmetrical structure consisting of an octamer of the two subunits, A8B8 (1).