Carnation Petal Membranes: A Study of Surface Properties Using Dansyl Pyrrolidine, a new Fluorescent Probe

Abstract

Summary Dansyl pyrrolidine (DNSP), a planar fluorophore that can be used for depolarization measurements, partitions into the surface regions of carnation membranes. Its partitioning constant (Kpart), representing the amount of membrane protein at 50 % partitioning of the probe between the aqueous and membrane lipid compartments, was 150 mg · L−1. Fluorescence spectra in membranes and triacetin had comparable maxima (490–500 nm), although the membrane spectra were broader indicating dielectric heterogeneity of the labelled region of the membrane. The fluorescence maxima also indicated that the fluorophore localizes in a relatively hydrophobic region of the membrane, dielectrically equivalent to about 90 % dioxane. Nevertheless, DNSP was found to lie close to the membrane surface, presumably in the hydrocarbon region just beneath the phospholipid head groups, as evidenced by its full quenching upon addition of quaternary N-methyl picolinium and N-methyl nicotinamide, both of which cannot access the membrane interior. Comparative depolarization data for 1,6-diphenyl-1,3,5-hexatriene (DPH) and DNSP labelled membranes indicate that lipid fluidity is higher in the DNSP labelled regions than deep within the bilayer interior. An Arrhenius plot of anisotropy determined with DNSP featured a marked discontinuity at 24°C for carnation microsomes, while the corresponding plot for DPH-labelled membranes exhibited no such discontinuities. Membrane regidifying effects of Ca2+ and trehalose were detected by DNSP, but not by DPH. Both probes showed lower fluidity in membranes and liposomes isolated from older flowers. Thus DNSP appears to have considerable potential as a probe for fluorescence depolarization measurements of membrane surfaces.