Studies on the denaturation of biological macromolecules by chemical carcinogens III. Optical rotatory dispersion and light-scattering changes of ovalbumin during denaturation and aggregation by water-soluble carcinogens

• 1.

  1. Optical rotatory dispersion and light-scattering measurements have been used for an investigation of the protein-denaturing ability of the water-soluble carcinogens, dimethylnitrosamine, diethylnitrosamine, ethylcarbamate, and dioxane.

• 2.

  2. It is found that each of these carcinogens produces a helix-coil transition in ovalbumin, as revealed by the change in b₀ of the Moffitt-Yang equation. The reduced, non-carcinogenic derivative of dimethylnitrosamine, dimethylhydrazine, is unable to produce this unfolding in the ovalbumin molecule. The helix content of ovalbumin in dioxane measured as a function of time indicates an unfolding and partial refolding of the protein.

• 3.

  3. Calculations of molecular weight from the light-scattering measurements show the formation of aggregates consisting of 2–9 ovalbumin molecules, for the range of denaturant concentrations used here. The magnitude of the time-dependent refolding of ovalbumin in dioxane appears to be limited by the aggregation process, since the helix content of ovalbumin in concentrated dioxane solution is not as high as is generally observed for other proteins and polypeptides in this solvent.

• 4.

  4. Alteration of hydrophobic bonding alone in ovalbumin cannot account for the denaturing ability of these carcinogens, rather the results support the proposal of hydrogen bonding between the agent and functional groups of the protein.