Biophysical Journal 49: 1089-1100 (1986)
© 1986 the Biophysical Society

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Papp, E. Articles by Meszéna, G. Search for Related Content PubMed Articles by Papp, E. Articles by Meszéna, G.

Electrodichroism of Purple Membrane

Ionic Strength Dependence

ABSTRACT

The dichroism of purple membrane suspension was measured in dc and ac electric fields. From these measurements three parameters can be obtained: the permanent dipole moment, µ, the electrical polarizability, , and the retinal angle, , (relative to the membrane normal). The functional dependence of the dichroism on the electric field is analyzed. There is a small decrease (2°) in retinal angle going from dark adapted to the light adapted form. No measurable difference in µ, , and was found under the photocycle. The dichroism was measured in two different salt solutions (KCl and CaCl₂) in the range 0-10 mM. The retinal angle increases from 64° to 68° with increasing ionic strength going through a minimum. This is attributed to the changing (decreasing) inner electric field in the membrane. The polarizability, , consists of two parts. One component is related to the polarization of the purple membrane and the second component to the ionic cloud. The second component decreases with ion concentration approximately as ^-3 ( is the Debye parameter) in agreement with a model calculation for the polarization of the ionic cloud. The origin of the slightly ionic strength dependent permanent dipole moment is not well understood.