  Some low-energy manifestations of a minimal extension of the Standard Model
based on the quark-lepton $SU(4)_V \otimes SU(2)_L \otimes G_R$ symmetry of the
Pati-Salam type are analysed. Given this symmetry a new type of mixing in the
quark-lepton interactions is shown to be required. An additional arbitrariness
of the mixing parameters could allow to decrease noticeably the lower bound on
the leptoquark mass $M_X$ originated from the $\pi$ and $K$ decays and the $\mu
e$ conversion. The only mixing independent bound emerging from the cosmological
limit on the $\pi^0 \rightarrow \nu \bar{\nu}$ decay width is $M_X > 18~TeV$.
