Osmotic perturbations induce differential movements in the core and periphery of proteins, membranes and micelles

Polymeric structures, namely, micelles, membranes and globular proteins sha re the property of two distinct regions: a hydrophobic core and a hydrophil ic exterior. The dynamics of these regions of the polymeric structures were probed using selective fluorophores 1,6-diphenyl-1,3,5-hexatriene (DPH) an d 1-anilinonaphthalene-8-sulfonate (ANS), respectively. Perturbation of the polymers by external osmotic pressure, ionic strength and temperature was monitored in the two regions using steady state measurements of fluorescenc e intensity and anisotropy. While :he fluorescence lifetime of DPH and ANS dib not change significantly, parallel change in steady state anisotropy va lues and the rotational correlation time indicated mobility in the probe/pr obe-domain. Osmotic perturbation of :he polymers in electrolyte media led t o decreased DPH mobility. Enhanced ellipticity at 222 nm in bovine serum al bumin was observed in 1.5 M NaCl and sucrose media. ANS exhibited a decreas ed anisotropy with progressive dehydration in proteins in NaCl media, in di myristoylphosphatidylcholine (DMPC) vesicles in sucrose media, and in neutr al laurylmaltoside micelles in both NaCl and sucrose media. Thus, ANS showe d responses opposite to that of DPH in these systems. A comparison with sev eral domain selective probes indicated that DPH reported findings common to depth probes while ANS reported data common to interfacial probes used for voltage monitoring. (C) 2001 Elsevier Science B.V. All rights reserved.