FOLDING STUDIES OF SINGLE TRP MUTANTS OF RNASE A

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We have made a mutant of Ribonuclease A which contains a single tryptophan residue (Trp92). This mutant has known fluorescent properties which can probe conformational changes associated with thermal unfolding. We have induced a 190C temperature jump in a pH 4.5 solution of Y92W using a 10 mJ ns pulse (1.5 ?m) from the ns OPO; the fluorescence from the Trp residue (at 340 nm) in the mutant is monitored at times from -500 ns before the T-jump to 30 ms after the T-jump. The static temperature of the protein solution was adjusted from 250C to 550C (through the melting curve). The data support that no significant perturbation surrounding the Trp residue is evident on timescales shorter than 30 ms. In addition, a significant difference in the increase of fluorescent intensity between temperature denaturation and GuHCl denaturation is also evident, suggesting differing mechanisms for denaturation.