  Deep inelastic scattering data on $F_2$ structure function obtained in the
fixed-target experiments were analysed in the valence quark approximation with
a next-to-next-to-leading-order accuracy. Parton distribution functions are
parametrized by using information from the Gottfried sum rule. The strong
coupling constant is found to be $\alpha_s(M_Z^2) = 0.1180 \pm
0.0020~\mbox(total\,exp.error)$, which coincides very well with the average
world value $\alpha_s^{\rm PDG}(M_Z^2) = 0.1181 \pm 0.0013$ updated recently in
a PDG report. The result for the second moment of the difference in $u$ and $d$
quark distributions $<\!\!x\!\!>_{u-d}=0.187 \pm 0.021$ is seen to be well
compatible with the latest LATTICE result $<\!\!x\!\!>_{u-d}^{\rm
LATTICE}=0.208 \pm 0.024$
