  It is shown that, if isospin is not conserved in $a^0_0$- and $f_0$-meson
mixing, forward-backward asymmetry arises in the reaction $pn\to da^0_0$. This
effect increases near the reaction threshold. The asymmetry is estimated within
the framework of a model in which the $a^0_0$-$f_0$ mixing is due to the
virtual $\pi^0\leftrightarrow\eta$ transition and the difference in masses of
the charged and neutral kaons in decay channels. The angular asymmetry near the
threshold of the $pn\to da^0_0$ reaction was found to be large, of the order of
$8\div 15$ %.
