Gating and conductance changes in BK(Ca) channels in bilayers are reciprocal.

The energy associated with a mismatch between the hydrocarbon portions of a lipid bilayer and the hydrophobic regions of a transmembrane protein requires that one or both components deform in an attempt to minimize the energy difference. Transmembrane potassium channel subunits are composed of different structural motifs, each responsible for ion-selectivity, conductance and gating capabilities. Each has an inherent degree of flexibility commensurate with its amino acid composition. It is not clear, however, how each structural motif will respond to a fixed amount of distortion applied to the whole structure. We examined the single-channel conductance (G(c)) and gating (open probability, P (o)) of single BK(Ca) channels (hslo alpha-subunits) inserted into planar lipid bilayers containing 1,2-dioleoyl-3-phosphatidylethanolamine (DOPE) or DOPE with either 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) or sphingomyelin (SPM) and 1-palmitoyl-2-oleoyl-3-phosphatidylethanolamine (POPE) with SPM. These latter three binary mixtures formed stable membranes with different distributions of thickness domains as determined by atomic force microscopy. Channels placed in each composition should be exposed to different amounts of distortion. BK(Ca) channels forced into the DOPE/SPM bilayer containing lipid domains with two different thicknesses showed two distinct levels of G(c) and P(o). The alterations in G(c) and P(o) were reciprocal. A larger conductance was accompanied by a smaller value for gating and vice versa. Channels forced into the POPE/SPM bilayer containing lipid domains with different thicknesses showed more than two distinct levels of G(c) and P(o). Channels placed in a uniform bilayer (DOPE/DOPC) showed a uniform distribution of conductance and activation. We conclude that both the inner and outer domains of the channel where these two channel functions are localized respond to deformation and that a fixed amount of distortion results in reciprocal changes in protein function.

Photochemical pinacol rearrangements of unsymmetrical diols.

The photochemical pinacol reaction of a series of nonsymmetrical 9-fluorenyl-substituted vic-diols was investigated and compared with their acid-catalyzed thermal reaction. Unlike the thermal reaction, the radiation-induced processes involve only fluorenyl cations, as is reflected in differences of product distribution between the two reactions. From the product studies, substituent migratory aptitudes are reversed in the photochemical process, suggesting that kinetic control takes place under neutral conditions unlike the acid-catalyzed thermal reactions. The presence of fluorenyl cation intermediates and their lifetimes were established by laser flash spectroscopy studies.

Probing the binding dynamics to sodium cholate aggregates using naphthalene derivatives as guests.

The binding dynamics with bile salt aggregates for a series of naphthalene derivatives of different polarities was studied using fluorescence and laser flash photolysis. Fluorescence was employed to determine the nature of the binding site for each guest and the accessibility of the bound guest to quenchers. Laser flash photolysis was employed to study the mobility of the triplet states of the naphthalenes between the sodium cholate aggregates and the aqueous phase. Primary aggregates, which provide an environment protected from quenchers in the aqueous phase, bind 1- and 2-ethylnaphthalene as guests. The complexation dynamics with this type of aggregate is slow. 1- and 2-Naphthyl-1-ethanol, and 1- and 2-acetonaphthone bind to the secondary aggregates, which provide moderate protection from quenching and faster binding dynamics. The addition of salts lowered the cholate concentration at which primary aggregates were formed, but did not influence the formation of secondary aggregates.