MOLTEN GLOBULAR CHARACTERISTICS OF THE NATIVE STALE OF APOMYOGLOBIN

Apomyoglobin, myoglobin lacking the haem group, is a natural intermedi ate in biosynthesis of myoglobin, and has some structural features in common with the haem-containing native state. Unfolding or refolding s tudies of apomyoglobin have identified a molten globule intermediate a t acid ph. We show here that both the native state of apomyoglobin and the molten globule intermediate have highly plastic structures. Subst itution of single amino acids on the surface or in the interior of hel ices in the native protein produce dramatic changes in the helix conte nt and tryptophan emission of apomyoglobin at neutral and acidic ph. T he signals from the intermediate and native apomyoglobin correlate clo sely suggesting that apomyoglobin itself has a molten globule-like cha racter its structure representing a population of interconverting subs tates rather than a fixed conformation.