Propionyl-coenzyme A carboxylase of Mycobacterium smegmatis. An electron microscopic study

Propionyl-CoA carboxylase has been purified to homogeneity and examined in electron microscope. The native carboxylase presents a profile with a large central subunit to which smaller subunits are attached. The central subunit has two prominent profiles, one circular (100 A) with a central hole and the other rectangular (70 X 100 A). The six polypeptides of this subunit appear to be arranged in a cylindrical structure. Six spherical (50 A) biotin-containing peripheral subunits are attached in sets of three to the two opposite circular faces of the central subunit. A model of the 18-S carboxylase is presented.