  We propose a symmetry of the Dirac equation under the interchange of signs of
eigenvalues of the Dirac's $K$ operator. We show that the only potential which
obeys this requirement is the Coulomb one for both vector and scalar cases.
Spectrum of the Dirac Equation is obtained algebraically for arbitrary
combination of Lorentz-scalar and Lorentz-vector Coulomb potentials using the
Witten's Superalgebra approach. The results coincides with that, known from the
explicit solution of the Dirac equation.
