We have studied the effect of melittin, a basic membrane-binding peptide, on Ca-ATPase activity and on protein and lipid dynamics in skeletal sarcoplasmic reticulum (SR), using time-resolved phosphorescence and fluorescence spectroscopy. Melittin completely inhibits Ca-ATPase activity, with half-maximal inhibition at 9 +/- 1 mol of melittin bound to the membrane per mole of ATPase (0.1 mol of melittin per mole of lipid). The time-resolved phosphorescence anisotropy (TPA) decay of the Ca-ATPase labeled with erythrosin isothiocyanate (ERITC) shows that melittin restricts microsecond protein rotational motion. At 25 degrees C in the absence of melittin, the TPA is characterized by three decay components, corresponding to a rapid segmental motion (correlation time phi 1 = 2-3 microseconds), the uniaxial rotation of monomers or dimers (phi 2 = 16-22 microseconds), and the uniaxial rotation of larger oligomers (phi 3 = 90-140 microseconds). The effect of melittin is primarily to decrease the fraction of the more mobile monomer/dimer species (A2) while increasing the fractions of the larger oligomer (A3) and very large aggregates (A infinity). Time-resolved fluorescence anisotropy of the lipid-soluble probe diphenylhexatriene (DPH) shows only a slight increase in the lipid hydrocarbon chain effective order parameter, corresponding to an increase in lipid viscosity that is too small to account for the large decrease in protein mobility or inhibition of Ca-ATPase activity. Thus the inhibitory effect of melittin correlates with its capacity to aggregate the Ca-ATPase and is consistent with previously reported inhibition of this enzyme under conditions that increase protein-protein interactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental results demonstrate that the fluorescent probes 2-(N-hexadecylamino)-naphthalene-6-sulfonate (HANS) and 2-(N-decylamino)-naphthalene-6-sulfonate (DANS) are solubilized in two distinct regions, that is, the headgroup and core, within micelles of cetyltrimethylammoniumbromide (CTAB), tetradecyltrimethylammoniumbromide (TTAB), dodecyltrimethylammoniumbromide (DTAB), cetyltrimethylammoniumchloride (CTAC), and tetradecyltrimethylammoniumchloride (TTAC). The fluorescence lifetime decays for both chromophores are biexponential in all the different micelles. The population associated with the shorter lifetime (τ 1 = 4-5 ns) is located in the Stern layer, where reduction of the fluorescence lifetime occurs because of quenching induced by the bromide counterions. The second population of chromophores is located in the hydrocarbon core region of the micelle. In this environment the chromophores have a considerably longer lifetime (τ 2 = 19-20 ns) because there is no significant quenching by bromide counterions. Evidence of water penetration places them fairly close to the core-Stern layer interface. Time-dependent fluorescence anisotropy is analyzed in terms of these two populations. The measurements show that the orientational relaxation of the probes in the hydrocarbon core region is considerably slower than orientational relaxation in the Stern layer. When the lifetime measurements and the orientational relaxation measurements are combined, the partitioning of the chromophores in the core and headgroup regions of the micelles can be determined.

The temperature dependent dynamics of polydimethylsiloxane (PDMS) melts are investigated by measuring orientational relaxation of a dissolved probe molecule, 2-naphthyltriethoxysilane (NTES) using time resolved fluorescence depolarization. The temperature dependent viscosity of PDMS is also reported for two molecular weights. The measurements of nonpolar NTES probe dynamics are compared to previous measurements on the polar probe, N-(triethoxysilylpropy1)dansylamide. The activation energies for the orientational relaxation of the two probes arevery different. This is discussed in terms of the influence of the polarity of the solutes on the local structure in the melts. The results have implications for possible modifications of the physical properties of PDMS materials by using solutes or side groups of varying polarity. The synthesis of the NTES probe, which can also be used as a cross-linking reagent for PDMS, is also described.

A Monte Carlo simulation of polymer/polymer interface in the presence of block copolymer. I. Effects of the chain length of block copolymer and interaction energy Monte Carlo ͑MC͒ simulations of electronic excitation transfer ͑EET͒ among a small number of chromophores covalently incorporated into copolymer molecules are presented and used to test the results of previously developed analytical EET theories that are useful for the study of polymer chain structure ͓K. A. Peterson and M. D. Fayer, J. Chem. Phys. 85, 4702 ͑1986͔͒ and phase separation in polymer blends ͓A. H. Marcus and M. D. Fayer, J. Chem. Phys. 94, 5622 ͑1991͔͒. The simulations and theory account for EET among chromophores bound to a single chain and among chromophores attached to different chains. The calculated quantity, ͗G s (t)͘, which is the probability that an initially excited chromophore is still excited at time t, is related to time-resolved fluorescence depolarization experiments. The theories, particularly the treatment of interchain EET, depend on a series of approximations whose efficacy has not been determined. Close agreement between the MC simulations and the analytical theory are found for a variety of situations, including those that mimic real polymer systems. The limits beyond which agreement is weakened provide specific guidelines for the design of polymer structure and phase-separation experiments.