Application of CHAPS-PC detergent to determine rhodopsin absorbance spectra in squids

The utility of CHAPS-PC, a detergent combination for solubilizing membrane proteins, was investigated as a substitute to digitonin solution for extracting rhodopsin in the measurement of spectral sensitivity in squid. Microvilli of the photoreceptor outer segments were collected and purified from the retinas of three species, Uroteuthis edulis , Todarodes pacificus , and Heterololigo bleekeri , using sucrose density-gradient centrifugation. The difference in the absorption maximum ( λ max ) of rhodopsin between extraction with CHAPS-PC or with digitonin was 0–3 nm for all species. The λ max values of the three squid species were 488–490, 478–480, and 488–491 nm, respectively, which aligns well with values reported in previous studies. CHAPS and PC are less expensive than digitonin, which is advantageous when conducting repeated experiments. We hope that the present procedure for the extraction of visual pigments offers an improved fisheries technology that will be used to better understand the ecology of diverse squid species.