Dust-to-gas mass ratio and metallicity radial profiles of NGC 4254, NGC 4303, NGC 4321, and NGC 4501 with the oxygen abundance calibrated with KK04. The conversion factors X_CO are: with the Galactic conversion factor (dot-dashed red curve), with the linear metallicity dependence as in Eq. (1) (dotted green curve), with the superlinear dependence on metallicity as in Eq. (2) (dashed blue curve). The magenta circles are the oxygen abundance converted to the dust-to-gas scale with Eq. (3). For NGC 4254 and NGC 4321 we used the recalculation by Moustakas et al. (2010), for NGC 4303 and NGC 4501 the oxygen abundances by Skillman et al. (1996) converted to the KK04 scale. The continuous black lines show the fit to the abundance data.