The recently introduced nuclear Fukui function phi(alpha) is formally identified as a reactivity index of the density functional theory (according to the postulated criterion of d mu) and is shown to constitute the conformational contribution to a change in the molecular electronic chemical potential mu, through the relation d mu(N) = integral f(r)dv(r)dr=-Sigma(alpha)phi(alpha)dR(alpha), with phi(alpha)=(partial derivative F-alpha/partial derivative N)(nu)=-(delta mu/delta R(alpha))(N), where N is the number of electrons, f(r) the electronic Fukui function, v(r) the external potential at point r, R(alpha) the space coordinate of nucleus alpha, and F-alpha the force on nucleus alpha. Scaling of the nuclear coordinates with a factor lambda, as a particular conformational change, links the nuclear Fukui function with Berlin’s binding function B(r) for polyatomic molecules, d mu(lambda)(N)=d lambda integral f(r)B(r)dr=-Sigma(alpha)phi(alpha)dR(alpha)(lambda). This relation is instructing for interpretative purposes : changes in electron density are weighted by the binding function, which according to Berlin’s theorem, separates the system in binding and antibinding regions.