FORMATION OF A MOLTEN GLOBULE INTERMEDIATE EARLY IN THE KINETIC FOLDING PATHWAY OF APOMYOGLOBIN

Hydrogen exchange pulse labeling and stopped-flow circular dichroism w ere used to establish that the structure of the earliest detectable in termediate formed during refolding of apomyoglobin corresponds closely to that of a previously characterized equilibrium molten globule. Thi s compact, cooperatively folded intermediate was formed in less than 5 milliseconds and contained stable, hydrogen-bonded secondary structur e localized in the A, G, and H helices and part of the B helix. The re mainder of the B helix folded on a much slower time scale, followed by the C and E helices and the CD loop. The data indicate that a molten globule intermediate was formed on the kinetic folding pathway.