The circular dichroism of suspensions of frog rod outer segments.

The circular dichroism (CD) of suspensions of frog rod outer segments has been measured. At wave-lengths between 600 and 400 nm1. The suspensions show a large positive CD increasing towards shorter wave-lengths and largely unaffected by bleaching. This probably arises, at least in part, from the preferential scattering of one form of circularly polarized light.2. There is a small reduction in CD on bleaching, slightly larger but similar in sign and wave-length dependence to that shown by pigment extracts. At wave-lengths between 250 and 220 nm3. The suspensions show a CD somewhat similar in sign, magnitude and wave-length dependence to that given by pigment extracts.4. On bleaching there is a reduction of the negative CD at 225 nm again similar to that which takes place when extracts are bleached. The observations suggest that configurational changes, of the kind detected by CD, occur in the bleaching of rhodopsin molecules whether they are present in solutions or in rods.