Results. We find correlations between M-H2 and L-B, D-25(2), L-K, and L-FIR. The tightest correlation of M-H2 holds with L-FIR and, for T = 3-5, with L-K, and the poorest with D-25(2). The correlations with L-FIR and L-K are very close to linearity. The correlation with L-B is nonlinear so that M-H2/L-B increases with L-B. The molecular and the atomic gas masses of our sample show no strong correlation. We find a low mean value, log(M-H2/M-HI) = -0.7 (for T = 3-5), and a strong decrease in this ratio with morphological type. The molecular gas column density and the surface density of the star formation rate (the Kennicutt-Schmidt law) show a tight correlation with a rough unity slope. We compare the relations of M-H2 with L-B and L-K found for AMIGA galaxies to samples of interacting galaxies from the literature and find an indication for an enhancement of the molecular gas in interacting galaxies of up to 0.2-0.3 dex.