MULTIPLE INTERMEDIATES AND TRANSITION-STATES DURING PROTEIN UNFOLDING

Rapid kinetic studies of the unfolding of the small protein barstar by urea have been used to demonstrate the presence of at least two unfol ding intermediates on two competing unfolding pathways. One intermedia te has native-like secondary structure but has a partially solvated hy drophobic core, while the other is devoid of considerable secondary st ructure but has an intact hydrophobic core. It is shown that the trans ition states on the two pathways are very dissimilar structurally, but very similar energetically.