  A closed densely defined operator $ T $ on a Hilbert space $ \mathcal{H} $ is
callled $M$-hyponormal if $\mathcal{D}(T) \subset \mathcal{D}(T^{*}) $ and
there exists $ M > 0 $ for which $ \parallel(T-zI)^{*}x \parallel \leq M
\parallel(T-zI)x \parallel $ for all $ z \in \mathbb{C}$ and for all $ x\in
\mathcal{D}(T)$. In this paper, we prove that if bounded linear operator $ A :
\mathcal{H} \rightarrow \mathcal{K}$ is such that $ AB^*\subseteq TA $, where $
B $ is a closed subnormal (resp. a closed $ M $-hyponormal) on $\mathcal{H}$, $
T $ is a closed $ M $-hyponormal (resp. a closed subnormal) on $\mathcal{H}$,
then (i) $ AB\subseteq T^*A, $ (ii) $ {\overline{ran(A^{*})}} $ reduces $ B $
to the normal operator $ B\vert_{{\overline{ran(A^{*})}}}, $ and (iii) $
{\overline{ran(A)}} $ reduces $ T $ to the normal operator $
T\vert_{{\overline{ran(A)}}}.$
