  It is inferred from bulk-sensitive muon Knight shift measurement for a
Bi$_{1.76}$Pb$_{0.35}$Sr$_{1.89}$CuO$_{6+\delta}$ single-layer cuprate that
metal-insulator (MI) transition (in the low temperature limit, $T\rightarrow0$)
occurs at the critical hole concentration $p=p_{\rm MI}=0.09(1)$, where the
electronic density of states (DOS) at the Fermi level is reduced to zero by the
pseudogap irrespective of the N\'eel order or spin glass magnetism.
Superconductivity also appears for $p>p_{\rm MI}$, suggesting that this feature
is controlled by the MI transition. More interestingly, the magnitude of the
DOS reduction induced by the pseudogap remains unchanged over a wide doping
range ($0.1\le p\le0.2$), indicating that the pseudogap remains as a hallmark
of the MI transition for $p>p_{\rm MI}$.
