Fourier transform infrared study of photoreceptor membrane. I. Group assignments based on rhodopsin delipidation and reconstitution

Fourier transform infrared spectroscopy has been used to study the structure of bovine photoreceptor membrane. Rhodopsin appears to contain an extensive alpha-helical structure which is arranged predominantly perpendicular to the membrane plane. Spectra of delipidated rhodopsin and rhodopsin membranes reconstituted from dioleyl-phosphatidylcholine were compared with native photoreceptor membrane from rod outer segments in order to facilitate peak assignments. It is concluded that spectroscopic peaks characteristic of several protein and lipid groups can be assigned. We also find delipidation leads to alteration of the rhodopsin structure which is restored upon reconstitution. Membranes both suspended in ²H₂O and dehydrated were compared in order to detect possible conformational differences. Dehydration does not appear to grossly alter rhodopsin structure, although it may affect delipidated rhodopsin.