Normalized excitation and emission spectra obtained in HBS or methanol for (A) XAC-dansyl (50 µM), (B) XAC-X-Texas Red (1 µM) and (C) XAC-X-BY630 (1 µM). Data have been normalized to the maximum excitation or emission obtained with each ligand in methanol. Excitation maxima were: (A) 320, 315 nm; (B) 590, 585 nm and (C) 628, 634 nm in HBS and methanol respectively. Corresponding emission maxima were: (A) 500, 525 nm; (B) 605, 600 nm and (C) 645, 640 nm. The relative maximal emission intensities (HBS; methanol) were: (A) 0.26; (B) 0.89 and (C) 0.07. HBS, N-2-Hydroxyethylpiperazine-N′-2-ethanesulfonic acid-buffered saline; X, 6-aminohexanoyl; XAC, xanthine amine congener.