Fly photoreceptors. I. Physical separation of two visual pigments in Calliphora retinula cells 1-6

The two peaks of the spectral sensitivity curves of Calliphora correspond to two visual pigments. The peak sensitivity to polarized light for the u. v. sensitive pigment is at an angle to that for the green-sensitive pigment. The change in angle of the maximum polarization sensitivity as a function of wavelength occurs near 400 nm; in this transition the curves do not follow a cos2 function. The angle between the two maxima is different for each retinula cell. The only explanation of this phenomenon is that there are two visual pigments in different parts of the receptor, and one part is twisted relative to the other. There are therefore two metarhodopsins and the adaptation mechanisms are partially separate for the two peaks of the spectral sensitivity. The inference of two separated pigments modifies the interpretation of much previous work on fly photoreceptors