  Reparametrization invariant dynamics on a sphere, being parameterized by
angular momentum coordinates, represents an example of noncommutative theory.
It can be quantized according to Berezin-Marinov prescription, replacing the
coordinates by Pauli matrices. Following the scheme, we present two
semiclassical models for description of spin without use of Grassman variables.
The first model implies Pauli equation upon the canonical quantization. The
second model produces nonrelativistic limit of the Dirac equation implying
correct value for the electron spin magnetic moment.
