A Method for Calculation of Solvent Accessibility of Aromatic Amino Acid Residues of Proteins in Water--Organic Mixtures

A. A. Shevchenko¹ and O. A. Kost^1,2

¹School of Chemistry, Lomonosov Moscow State University, Moscow, 119899 Russia; fax: (7-095) 939-35-89.

²To whom correspondence should be addressed.

Submitted February 21, 1996; revision submitted July 19, 1996.

A method for calculation of solvent accessibility of tryptophan and tyrosine residues of a protein in water--organic mixtures based on second derivative UV spectra is suggested. The second derivative spectra cam be used to distinguish the direct effect of an organic solvent on spectral characteristics of exposed aromatic amino acid residues in proteins from its effect on protein conformation. The method can be used for calculation of the exposure of tryptophan residues in water--organic mixtures for proteins containing no more tyrosine residues than tryptophan residues. A similar method for calculation of the exposure of tyrosine residues can be used for proteins with tyrosine content at least fivefold exceeding that of tryptophan. As an example, the solvent accessibility of tryptophan residues in chymotrypsin is calculated in the presence of various organic solvents, e.g., ethanol, dioxane, and dimethyl formamide.

KEY WORDS: solvent accessibility, water--organic media, derivative spectroscopy, tryptophan, tyrosine.

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