J-aggregation of anionic ethyl meso-thiacarbocyanine dyes induced by binding to proteins.
The effects of ribonuclease A (RNase), lysozyme, trypsin, and bovine serum albumin (BSA) on the J-aggregation behavior of 3,3'-bis[sulfopropyl]-5-methoxy-4',5'-benzo-9-ethylthiacarbocyanine (1), 3,3'-bis[sulfopropyl]-4,5,4',5'-dibenzo-9-ethylthiacarbocyanine (2), and 3,3'-bis[sulfopropyl]-5,5'-dimethoxy-9-ethylthiacarbocyanine (3) were studied in aqueous solution. The formation of J-aggregates at pH 6 is induced by RNase for 1-3, by lysozyme for 1 and 2, and by trypsin for 2. The formation of J-aggregates correlates with decay of the dimers and is supported by induced circular dichroism spectra. The concentration of J-aggregates for lysozyme/1 increases with an increase in the protein/dye concentration ratio, reaches a plateau, and then gradually decreases. J-aggregates are characterized by relatively weak fluorescence; e.g., Phi(f) = 0.01 for lysozyme/1, and by a small Stokes shift of 6-8 nm, indicating almost resonance fluorescence. J-aggregation proceeds in the range of seconds to minutes with sigmoidal type kinetic curves for trypsin/2 and nonsigmoidal kinetics in the other cases. The presence of BSA, in contrast to RNase, lysozyme, and trypsin, results in deaggregation of dimers of 1-3 and formation of bound monomers and exhibits intense fluorescence from the trans-monomer; e.g., Phi(f) = 0.22 for BSA/1. Generally, the binding of 1-3 to the proteins is a cooperative process, where the number of binding sites changes from n = 15 for lysozyme/1 to n = 6 for trypsin/2 and n = 0.3 and 1 for BSA/3.
Slavnova
Tatyana D
TD
Center of Photochemistry, Russian Academy of Sciences, 119421 Moscow, Russia.
Görner
Helmut
H
Chibisov
Alexander K
AK
D000042:Absorption; D002232:Carbocyanines / Q000737:chemistry*; D002942:Circular Dichroism; D004396:Coloring Agents / Q000737:chemistry*; D005456:Fluorescent Dyes; D007536:Isomerism; D008968:Molecular Conformation; D009113:Muramidase / Q000737:chemistry; D011485:Protein Binding; D011506:Proteins / Q000737:chemistry; D012260:Ribonucleases / Q000737:chemistry; D012710:Serum Albumin, Bovine / Q000737:chemistry; D014357:Trypsin / Q000737:chemistry
D002232:Carbocyanines; D004396:Coloring Agents; D005456:Fluorescent Dyes; D011506:Proteins; D012710:Serum Albumin, Bovine; D012260:Ribonucleases; D009113:Muramidase; D014357:Trypsin