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The Polar and Electrical Nature of Dye Binding Sites on Human Red Blood Cell Membranes.

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Technical rept. Sep 70-Jun 72,

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Red blood cell membranes were stained with indicator dyes and their metachromatic color changes were measured. Interpretation of these changes at pH 7.4 indicates that the average membrane binding site is strongly hydrophobic and somewhat negatively charged. At pH 3, the equilibrium of membrane-bound bromophenol blue BPB is shifted to the unprotonated side a direction opposite to the hydrophobic change, apparently owing to neighboring positive charges at the binding sites. By increasing the concentration of the anionic BPB or by the addition of the anionic detergent sodium lauryl sulfate these positive charges appear to be successively titrated, rendering the membrane binding sites electrically neutral at this pH. The average vacant binding site possesses forces that can perform chemical work on bound compounds catalysis or rate inhibition. Similar results were obtained when bromothymol blue BTB was used to stain RBC stromata at pH 7.4. The BTB equilibrium is apparently shifted to the protonated side by the forces hydrophobic andor negative electrostatic present at the binding sites. At higher dye concentrations this effect is more intense, suggesting that the first molecules to bind donate negative charges and change the electrical nature of the binding sites. By using these and other dyes, the dye binding sites of RBC membranes were titrated. Electroneutrality was observed near pH7. Author Modified Abstract

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  • Biochemistry

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