  It is shown that the N=4 superalgebra of the Dirac theory in Taub-NUT space
has different unitary representations related among themselves through unitary
U(2) transformations. In particular the SU(2) transformations are generated by
the spin-like operators constructed with the help of the same covariantly
constant Killing-Yano tensors which generate Dirac-type operators. A parity
operator is defined and some explicit transformations which connect the
Dirac-type operators among themselves are given. These transformations form a
discrete group which is a realization of the quaternion discrete group. The
fifth Dirac operator constructed using the non-covariant Killing-Yano tensor of
the Taub-NUT space is quite special. This non-standard Dirac operator is
connected with the hidden symmetry and is not equivalent to the Dirac-type
operators of the standard N=4 supersymmetry.
