SDS causes significant polar exposure of aromatic amino acids of enolase. The alpha-helix content remains unchanged. The enzyme lost all its activity. 2. The presence of 1 M K Br in enzyme solution results in a smaller increase of polarity of aromatic amino acids residues environment. The amount of alpha-helix does not decrease in comparison to native enzyme. Enzyme lost nearly 80% of its initial activity. 3. The extreme pH values and the presence of 6 M Gnd.HCl influence the whole structure of enolase. It is accompanied by a large polar shift of aromatic amino acids and significant decrease of alpha-helix content of the protein.