pKa of the protonated Schiff base of bovine rhodopsin. A study with artificial pigments.
Artificial bovine rhodopsin pigments derived from synthetic retinal analogues carrying electron-withdrawing substituents (fluorine and chlorine) were prepared. The effects of the electron withdrawing substituents on the pKa values of the pigments and on the corresponding Schiff bases in solution were analyzed. The data suggest that the apparent pKa of the protonated Schiff base is above 16. However, the alternative possibility that the retinal Schiff base linkage in bovine rhodopsin is not accessible for titration from the aqueous bulk medium cannot be definitely ruled out.
Department of Organic Chemistry, Weizmann Institute of Science, Rehovot, Israel.
G
G
Steinberg
M
M
Ottolenghi
M
M
Sheves
D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002417:Cattle; D006863:Hydrogen-Ion Concentration; D008956:Models, Chemical; D011487:Protein Conformation; D011522:Protons; D012243:Rhodopsin / Q000031:analogs & derivatives / Q000138:chemical synthesis / Q000737:chemistry*; D012545:Schiff Bases / Q000737:chemistry; D013053:Spectrophotometry
D011522:Protons; D012545:Schiff Bases; D012243:Rhodopsin