FLUORESCENCE POLARIZATION OF COMPLEXES OF 1-ANILINO-8-NAPHTHALENESULFONATE WITH BOVINE SERUM ALBUMIN . EVIDENCE FOR PREFERENTIAL ORIENTATION OF LIGAND

The rotational relaxation time 〈ρ〉 of the complexes of 1-anilino-8-naphthalenesulfonate with bovine serum albumin has been calculated from independent measurements of fluorescence polarization and lifetime for different values of ̅n, the average number of 1-anilino-8-naphthalenesulfonate molecules bound per molecule of bovine serum albumin. It increases from 105 ± 3 nsec at ̅n = 1 to 128 ± 3 nsec at ̅n = 5 when the wavelength of excitation is 366 nm, but remains constant at 105 nsec for all values of ̅n when excitation is at 436 nm. Depolarization by energy transfer in both the bovine serum albumin-1-anilino-8-naphtha lenesulfonate adsorbates and concentrated solutions of 1-anilino-8-naphthalenesulfonate in propylene glycol is wavelength dependent, transfer failing in both cases upon excitation at 436 nm. Energy transfer is therefore the origin of the apparent increase in 〈ρ〉 with 〈ρ〉. Analysis of the results according to the preceding paper shows that a model of preferential orientation of the 1-anilino-8-naphthaknesulfonate molecules in planes parallel to the equator of a prolate ellipsoid of axial ratio 4 accounts for the observations. © 1969, American Chemical Society. All rights reserved.