Structure of protein solutions. Part 2. Solutions of total protein of yeast Saccharomyces cerevisiae.

Water systems formed by total protein of yeast Saccharomyces cerevisiae and model systems on the basis of unfractionated casein were studied by viscosimetry and electron microscopy. Methodologically, both methods offered a possibility of distinguishing several quantitatively different concentration intervals in protein solutions under different conditions. Viscosimetry gave the most informative results at the concentration intervals where the solutions approached the true ones, while electron microscopy did so when supermolecular formations prevailed. In comparing the data obtained by these two methods the following conclusions were drawn: At low temperatures (4-10 degrees C) yeast protein was in molecular-dissociated condition. Association in the system starts at 10 degrees C, and becomes enhanced with a rise in temperature. A temperature rise to 25-30 degrees C promotes a more compact packing of polypeptide chains; further heating leads to high-temperature denaturation. Lipids induce covering of polypeptide chains and prevent associations, thus leading to an increase in the system's thermostability.