Membrane Potentials and Permeability of Ions for Bombyx Mori Fibroin Membrane

Abstract

The concentration membrane potentials of Bombyx mori fibroin membrane by chlorides, bromides, iodides and nitrates of potassium and sodium and the permeation rates of these salts through the membrane were measured. The fibroin membrane used was prepared by dissolving a degummed cocoon fibre in a lithium bromide solution : it becomes insoluble in water by treatment with ethyl alcohol. The membrane potential increases according to the sequences : I>NO3> Cl and K>Na. These sequences can be correlated to the adsorption of these ions to the fibroin molecules. The isoelectric point of fibroin, which is obtained from the membrane potentials, is pH 4. 2. The permeability of the salts also increases according to the sequences : I>NO3> Cl and K>Na. However, these sequences depend on the degree of swelling of the membrane, which is due to the adsorption of the anions, and on the size of ionic radius of the hydrated cations. The permeability of potassium chloride becomes minimum in the vicinity of isoelectric point of the membrane. The mechanism of ion permeation through the membrane was discussed by Nagasawa and Kobatake's theory. © 1973, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.