Perhaps you should try some spelling variations:
"photoeffector proteins" » "photoreceptor proteins", "effector proteins", "photoreceptor protein"
"photoreceptor pigments" » "photoreceptor proteins"
"receptor proteins" » "receptor protein", "effector proteins"

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (((("photoeffector proteins") OR ("receptor proteins"))) OR ("photoreceptor pigments")).
• Removing quotes may allow a broader search: (((( photoeffector proteins ) or ( receptor proteins ))) or ( photoreceptor pigments )).
• Adding a wildcard symbol may retrieve word variants: (((("photoeffector proteins") or ("receptor proteins"))) or ("photoreceptor pigments"))*.