  Recently individual two-headed kinesin molecules have been studied in in
vitro motility assays revealing a number of their peculiar transport
properties. In this paper we propose a simple and robust model for the kinesin
stepping process with elastically coupled Brownian heads showing all of these
properties. The analytic and numerical treatment of our model results in a very
good fit to the experimental data and practically has no free parameters.
Changing the values of the parameters in the restricted range allowed by the
related experimental estimates has almost no effect on the shape of the curves
and results mainly in a variation of the zero load velocity which can be
directly fitted to the measured data. In addition, the model is consistent with
the measured pathway of the kinesin ATPase.
