This is the 2 state model of Myosin V movement described in the article: A simple kinetic model describes the processivity of myosin-v. Kolomeisky AB , Fisher ME Biophys. J. 84(3):1642-50 (2003); PubmedID: 12609867 Abstract: Myosin-V is a motor protein responsible for organelle and vesicle transport in cells. Recent single-molecule experiments have shown that it is an efficient processive motor that walks along actin filaments taking steps of mean size close to 36 nm. A theoretical study of myosin-V motility is presented following an approach used successfully to analyze the dynamics of conventional kinesin but also taking some account of step-size variations. Much of the present experimental data for myosin-V can be well described by a two-state chemical kinetic model with three load-dependent rates. In addition, the analysis predicts the variation of the mean velocity and of the randomness-a quantitative measure of the stochastic deviations from uniform, constant-speed motion-with ATP concentration under both resisting and assisting loads, and indicates a substep of size d(0) approximately 13-14 nm (from the ATP-binding state) that appears to accord with independent observations. The model differs slightly from the published version. The ATP and ADP bound forms of myosin are called S0 and S1. The state transition and binding constants are called k_1, k_2, k_3 and k_4 instead of k 0 0 , u 0 1 , k ' 0 and w 0 1 . Similarly the state loading factors are named th_1, th_2, th_3 and th_4 instead of θ + 0 , θ + 1 , θ - 0 and θ - 1 . The species fwd_step1, fwd_step2, back_step1 and back_step2 count the number of state changes of each kind the myosine molecules have taken over time. The model can be evaluated in a deterministic continuous or stochastic discreet fashion. The parameter V holds the (forward) speed at each time point, the V_avg the overall way divided by the simulation time and the amount of myosine molecules. Originally created by libAntimony v1.4 (using libSBML 3.4.1) This model originates from BioModels Database: A Database of Annotated Published Models (http://www.ebi.ac.uk/biomodels/). It is copyright (c) 2005-2011 The BioModels.net Team. For more information see the terms of use . To cite BioModels Database, please use: Li C, Donizelli M, Rodriguez N, Dharuri H, Endler L, Chelliah V, Li L, He E, Henry A, Stefan MI, Snoep JL, Hucka M, Le Novère N, Laibe C (2010) BioModels Database: An enhanced, curated and annotated resource for published quantitative kinetic models. BMC Syst Biol., 4:92.