The molten globular intermediate form in the folding pathway of human carbonic anhydrase B

The acid-induced and guanidinium chloride-induced conformational transitions in human carbonic anhydrase B have been analyzed. A structural form was detected at pH 3, which has a higher secondary structural order than the native enzyme but little tertiary structure. The enzyme dissolved in an intermediate concentration of the denaturant guanidinium chloride (1 M at pH 7.5) also adopts a similar conformational state. This form, denoted as the intermediate form I, possesses most of the characteristics defined for the molten globular state of globular proteins and might serve as the embryonic structural intermediate during the self-organization of the protein into its functional native form.