  One considers the quantum dynamics of a charged spin-1/2 particle in an
extended external eletromagnetic field that arises from the reduction of a
5-dimensional Abelian gauge theory. The non-relativistic regime of the reduced
4D-dynamics is worked out and one identifies the system as a sector of an
N=2-supersymmetric quantum-mechanical dynamics. The full supersymmetric model
is studied and one checks the algebra of the fermionic charges; the conclusion
is that no central charge drops out. The possible r\^ole of the extra external
fields, a scalar and a magnetic-like field, is discussed.
