Pyruvate carboxylase from Pseudomonas citronellolis: Shape of the enzyme, and localization of its prosthetic biotin group by electron microscopic affinity labeling

Pseudomonas citronellolis is known to contain a pyruvate carboxylase with α 4β 4 composition. All the other pyruvate carboxylases investigated so far are made up of four seemingly identical subunits. Nevertheless, this exceptional pyruvate carboxylase exhibits a size and overall shape similar to other pyruvate carboxylases. Electron microscopic affinity labeling with avidin revealed that the prosthetic biotin groups (one per αβ unit, i.e. four per enzyme particle) are located close to the inter-unit junctions of pairs of αβ units making up the enzyme. This position of the prosthetic biotin groups is very similar to the location of the biotin in the other carboxylases.