Bovine Serum Albumin as a Catalyst. III. Conformational Studies

We have used the recently discovered catalytic activity of bovine serum albumin (BSA) as a sensitive probe of the conformational properties of this protein in solution. When the protein is unfolded in 8 M urea and the disulfide bonds are broken with mercaptoethanol, as much as 73% of full activity can be regained if the protein is diluted and allowed to slowly air reoxidize and the monomer is isolated. Our evidence indicates that irreversible denaturation of the protein in 8 M urea alone is caused by an intermolecular reaction which must involve a disulfide exchange reaction which is facilitated by the free unprotonated sulfhydryl group of the protein. Irreversible thermal denaturation also is strongly aided by the free sulfhydryl group. The results of these and other experiments are in general agreement with recent theories about domain structure in proteins. The data suggest that certain domains in BSA have greater conformational stability than other domains. Our evidence indicates that the catalytic active site of the molecule is part of one domain of relatively high conformational stability.