Electric polarizabilities of proton and neutron and the relativistic center-of-mass coordinate

We argue that the relativistic correction $\delta {\mathbf{R}}_{c\mathrm{.}m\mathrm{.}}$ to the center-of-mass vector can lead to the approximate equality of the proton and neutron electric polarizabilities in the quark model. The explicit form of $\delta {\mathbf{R}}_{c\mathrm{.}m\mathrm{.}}$ depends only on the non-relativistic potential between quarks. In particular, this correction is the same for the potential generated by Lorentz-vector and -scalar interactions.