Microspectrophotometry of rhodopsin and metarhodopsin in the moth Galleria

Fresh, frozen sections of the photoreceptor layer of the compound eye of the moth Galleria have been examined by microspectrophotometry, using 4 X 8 mum measuring beams that sampled from approximately two to four rhabdoms. The principal visual pigmen: absorbs maximally at 510 nm (P510), and on irradiation is converted to a thermally stable, pH- insensitive metarhodopsin with lambdamax at 484 nm (M484) and a 43% increase in molar extinction coefficient. Subsequently, short wavelength irradiation of the metarhodopsin photoregenerates some P510; but the absence of an isosbestic point in the cycle of spectral changes is consistent with the presence of smaller amounts of violet- or ultraviolet-sensitive visual pigment(s) that also are converted to a blue-absorb g metarhodopsin. Difference spectra for both P510 and M484 were measured, using hydroxylamine. The 484-nm metarhodopsin is reversibly converted to a form with lambdamax at 363 nm by high concentrations of glycerol. Dark regeneration of rhodopsin in vivo after several minutes exposure of thoroughly dark-adapted animals to full sunlight requires several days.