We describe the formation of axial GaAs/AlAs heterostructured nanowires grown via the vapor-liquid-solid method. The calculations are based on the combination of mass balance of atoms in the droplet and the nucleation-limited composition of ternary AlxGa1-xAs nanowires. We examine the influence of growth temperature, atomic Al flux and the Au concentration in the liquid on the interfacial abruptness. In particular, we compare the compositional profiles of heterostructures in Au-catalyzed and self-catalyzed nanowires. The obtained results might be useful for growth of GaAs/AlAs heterostructured nanowires.