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**Stokes efficiency of molecular motor-cargo systems.**
*(English)*
Zbl 1141.92044

Summary: A molecular motor utilizes chemical free energy to generate a unidirectional motion through a viscous fluid. In many experimental and biological settings, a molecular motor is elastically linked to a cargo. The stochastic motion of a molecular motor-cargo system is governed by a set of Langevin equations, each corresponding to an individual chemical occupancy state. The change of the chemical occupancy state is modeled by a continuous time discrete space Markov process. The probability density of a motor-cargo system is governed by a two-dimensional Fokker-Planck equation. The operation of a molecular motor is dominated by high viscous friction and large thermal fluctuations from the surrounding fluid.

The instantaneous velocity of a molecular motor is highly stochastic: the past velocity is quickly damped by the viscous friction and the new velocity is quickly excited by bombardments of surrounding fluid molecules. Thus, the theory for macroscopic motors should not be applied directly to molecular motors without close examination. In particular, a molecular motor behaves differently working against a viscous drag than working against a conservative force. The Stokes efficiency was introduced to measure how efficiently a motor uses chemical free energy to drive against a viscous drag. For a motor without cargo, it was proved that the Stokes efficiency is bounded by 100%. Here, we present a proof for the general motor-cargo system.

The instantaneous velocity of a molecular motor is highly stochastic: the past velocity is quickly damped by the viscous friction and the new velocity is quickly excited by bombardments of surrounding fluid molecules. Thus, the theory for macroscopic motors should not be applied directly to molecular motors without close examination. In particular, a molecular motor behaves differently working against a viscous drag than working against a conservative force. The Stokes efficiency was introduced to measure how efficiently a motor uses chemical free energy to drive against a viscous drag. For a motor without cargo, it was proved that the Stokes efficiency is bounded by 100%. Here, we present a proof for the general motor-cargo system.

### MSC:

92E99 | Chemistry |

60J20 | Applications of Markov chains and discrete-time Markov processes on general state spaces (social mobility, learning theory, industrial processes, etc.) |

76D99 | Incompressible viscous fluids |

92E20 | Classical flows, reactions, etc. in chemistry |

92C40 | Biochemistry, molecular biology |

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