The Photochemical Equilibrium in Rhabdomeres of Eledone and Its Effect on Dichroic Absorption

Abstract

The preceding paper by TAUBER in this volume, showed by microphotometric measurements on the retina of Eledone moschata, that the photochemical equilibria between rhodopsin and metarhodopsin differ, depending on whether the pigment molecules are within rhabdomeres or in solution. This is especially so when polarized light is used. In this paper, we first theoretically analyse how photochemical equilibria and absorption depend on position and orientation of visual pigment molecules within the microvillar membrane (the orientation of the rhodopsin and metarhodopsin may differ), and on the angle of incidence and plane of the E-vector of linearly polarized light. In our considerations, which are intended to describe relatively slow measurements at room temperature, the short-lived intermediates which exist during the transitions between rhodopsin and metarhodopsin can be neglected. In the second part of this paper, the theoretically derived relations are used to interpret microphotometric measurements on sections of the retina of Eledone moschata and to draw conclusions on the orientation of rhodopsin and metarhodopsin within the microvillar membrane.