RECOGNITION OF AMINO-ACIDS BY MEMBRANE-POTENTIAL AND CIRCULAR-DICHROISM OF IMMOBILIZED ALBUMIN MEMBRANES

The shifts in membrane potential, caused by the injection of some amin o acids into a permeation cell, were measured using immobilized serum albumin membranes at isoelectric points of the amino acids. The effect ive fixed charge density was estimated to decrease after the injection of alanine, phenylalanine, and tryptophan and to increase after the i njection of serine. The change in the fixed charge density originated from the conformational change of the immobilized albumin membranes in duced by the binding between the albumin and amino acids in the membra nes, since the conformational change of the immobilized albumin membra nes induced by the binding of the amino acids to the serum albumin was observed from circular dichroism measurements. There was found, howev er, some discrepancy between the conformational change of the serum al bumin in the albumin membranes detected by the membrane potential meas urements and the circular dichroism measurements. This is explained by the fact that the circular dichroism measurements detect the increase or decrease in the alpha-helix, beta sheet, and random coil contents; however, they do not always contribute to the detection of the change in the charge density due to the presence of the amino acid in the al bumin membranes. (C) 1995 John Wiley & Sons, Inc.