The pH 6 Acetolactate‐Forming Enzyme from Aerobacter aerogenes

The diffusion and sedimentation constants of the pH 6 acetolactate‐forming enzyme, determined by analytical ultracentrifugation, were used to calculate a molecular weight of 200 000 for the enzyme. The amino acid composition of the enzyme has been worked out, and 3 molecules of cocarboxylase, and 6 atoms of phosphorus were found to be tightly bound to one molecule of the enzyme. In addition, the effect of divalent cations was studied, results indicated that the enzyme has a requirement for manganese. An absolute requirement for cocarboxylase and manganese was not established. Two crystalline forms of the enzyme were studied by electron microscopy using negative staining technique. The plate‐shaped crystals were composed of rows of particles measuring approximately 100 × 60 Å. These particles consisted of sub‐units, and in some areas a helical organization of the crystal could be seen. The molecular organization was different in the two different crystalline forms of the enzyme.