Permeability of Bombyx mori Fibroin Membrane to Some Sugars

Abstract

The permeation rates of glucose, sucrose and raffinose and that of potassium chloride in aqueous solutions through the fibroin membranes obtained from Bombyx mori cocoons were measured over the temperature range 5 to 90°C. From the plots of log Km•d/A vs. 1/T (Km: apparent permeation constant, d: thickness of membrane, A: effective area of membrane, T: absolute temperature) for the sugars and the potassium chloride, two transition points were found at temperatures near 25 and 65°C for the fibroin membrane these transition temperatures coincided with those obtained by dilatometric or viscoelastic measurements. The pores of the fibroin membrane through which the solutes can penetrate are narrower compared to those of cellulose membrane. The permeability of the fibroin membrane to a solute decreases rapidly with the increase in its molecular size. Measurements of pH dependence have revealed that the permeability to glucose becomes minimum in the vicinity of the isoelectric point of the membrane: in this case, the permeability is governed by the swelling of the membrane.