This review examines some recent applications of fluorescence recovery after photobleaching (FRAP) to biopolymers, while mainly focusing on membrane protein studies. Initially, we discuss the lateral diffusion of membrane proteins, as measured by FRAP. Then, we talk about the use of FRAP to probe interactions between membrane proteins by obtaining fundamental information such as geometry and stoichiometry of the interacting complex. Afterwards, we discuss some applications of FRAP at the cellular level as well as the level of organisms. We conclude by comparing diffusion coefficients obtained by FRAP and several other alternative methods.

No abstract

We report the first use of pressure perturbation calorimetry (PPC) to characterize the heat-induced helix-coil transition of DNA polymers. The alternating copolymer poly[d(A-T)] was studied in aqueous solutions containing 5.2 and 18.2 mM Na+; it exhibited helix-coil transition temperatures of 33.6 and 44.7 degrees C, respectively. The transition is accompanied by a negative molar volume change, DeltaV) -2.6 and -2.1 mL/mol (base pair), respectively, and an increase in the coefficient of thermal expansion, Deltaalpha=+5x10(-4) K(-1) (at both ionic strengths). These values are consistent with a greater hydration of the coil form. The larger water-accessible surface area of the coil causes more water molecules to assume a bound, more densely packed structure that then gradually decreases with increasing temperature, leading to a larger value of R. The magnitude of the volume changes detected by PPC were larger than those deduced from high-pressure UV spectroscopy, shedding light on the effect of pressure on DeltaV. The shape of the PPC peak was nearly identical to the shape of the DSC peak, providing direct evidence for the correlation between the molar volume change and enthalpy change for the helix to coil transition of DNA.