2026/06/18 by Nathaniel Wesnak, Markus Deserno · 1 voice
Biochemistry, Genetics and Molecular Biology · Physics and Astronomy · #Asymmetry #Binary number #Field (mathematics) #Lipid Membrane Structure and Behavior #Lipid metabolism and biosynthesis #Master equation #Mixing (physics) #Noise (video) #Relaxation (psychology) #Spectroscopy and Quantum Chemical Studies #Stochastic differential equation #Stochastic process
paper · doi:10.1063/5.0326588
published in The Journal of Chemical Physics 164(23) (American Institute of Physics)
openalex publication_date 2026/06/18 · openalex created_date 2026/06/19 · openalex updated_date 2026/06/26
Since lipid bilayers are self-assembled macroscopic aggregates, their constituent lipid molecules can spontaneously transition between the two leaflets. This so-called "flip-flop" is almost universally described via first-order chemical kinetics: the net "flux" leaving a given leaflet is proportional to the number of lipids it contains. However, this model ignores interactions, such as those arising from packing or non-ideal mixing, and restricting the analysis to macroscopic rate equations misses fluctuations. Here, we employ tools from the field of stochastic processes to examine the impact of stress and non-ideal mixing on lipid flip-flop, and we discuss several methods for quantifying the associated fluctuations-ranging from stochastic trajectories to evolution equations for probability densities. We show that differential stress strongly enhances the rate at which lipid abundance asymmetry decays, while compositional relaxation in mixed systems can be closer to ideal under suitable conditions. For the case of binary systems in the presence of packing constraints, we employ a linear noise approximation to the system's master equation and show that it leads to an easily manageable Ornstein-Uhlenbeck process for the fluctuations of (and correlations between) compositions. We also show how to include non-ideal mixing, which leads to large and very slow compositional fluctuations as we approach the critical point.