  The covariant quantization of massless D=11 superparticle (M0-brane) in its
twistor-like Lorentz harmonic formulation is used to clarify the origin and
some properties of the Berkovits pure spinor approach to quantum superstring
and to search for hidden symmetries of D=11 supergravity. In the twistor like
Lorentz harmonic formulation, the SO(16) symmetry is seen already at the
classical level. The quantization produces the linearized supergravity
multiplet as 128+128=256 component Majorana spinor of SO(16) and also shows an
indirect argument in favor of the possible E8 symmetry.
