Circular dichroic study of the conformational stability of sulfhydryl-blocked bovine serum albumin.

1. The blockage of the single sulfhydryl-group of bovine serum albumin does not alter the secondary structure, although the alpha-helical structure is destabilized since lower concentrations of guanidine and of urea unfold the protein. 2. What happens to the previously helical structure depends upon the reagent used to block the sulfhydryl-group. Bovine serum albumin derivatized with 5,5'-dithiobis-(2-nitrobenzoic acid) and iodoacetate preferentially acquire the beta-structure in high concentrations of guanidine and urea, whereas iodoacetamide-derivatized bovine serum albumin acquires primarily the random coil structure. 3. Part of the helical structure is also lost in 5-6 mM sodium dodecyl sulfate; thionitrobenzoate-bovine serum albumin shows an increase in the random coil, whereas the two alkylated proteins display the increase both in beta-structure and random coil. 4. Carboxymethylation or carboxamidomethylation of fully reduced bovine serum albumin results in a drastic change in the secondary structure of the protein with a substantial decrease in alpha-helix and a corresponding increase in both beta-structure and random coil. These extensively alkylated proteins also display differences in denaturation profiles in solutions of guanidine and urea.