We present a method for constructing new quadratic APN functions from known ones. Applying this method to the Gold power functions we construct an APN function x(3) + tr(x(9)) over F2(n). It is proven that for n >= 7 this function is CCZ-inequivalent to the Gold functions, and in the case n = 7 it is CCZ-inequivalent to any power mapping (and, therefore, to any APN function belonging to one of the families of APN functions known so far).