Osmotic Pressure Determinations with Isolated Protoplasmic Proteins.

LOEB (9), KUNTZ et al. (6), SCATCHARD et al. (11), and others have made use of osmotic pressure measurements to calculate the molecular weights of pure proteins such as gelatin, crystallized enzymes, and crystallized serum albumen. Protoplasmic proteins have not been investigated. Yet it would be of some interest to know the average molecular weight of a plant's protoplasmic proteins. Such information is essential if, for instance, one is to test theories of protein splitting at low temperature. Curves obtained by plotting pressure against concentration also yield information about the relative hydration ("bound water") of the protein, for as the concentration increases, a larger and larger portion of the pressure is due to the hydration rather than the number of molecules present. The adaptation of a plant to unfavorable environmental conditions is frequently ascribed to increased hydration of proteins (4). Evidence for such theories has heretofore been indirect; e.g., from measurements of protoplasmic viscosity or from the properties of plant juices which come mainly from the vacuole rather than the protoplasm (7). Methods