  Oxygen isotope (^{16}O/^{18}O) effects (OIE's) on the superconducting
transition (T_c), the spin-glass ordering (T_g), and the antiferromagnetic
ordering (T_N) temperatures were studied for Y_1-xPr_xBa_2Cu_3O_7-\delta as a
function of Pr content (0.0\leq x \leq 1.0). The OIE on T_c increases with
increasing x up to x\approx0.55, where superconductivity disappears. For
decreasing x the OIE's on T_N and T_g increase down to x\approx 0.7 where
antiferromagnetic order and down to x\approx0.3 where spin-glass behavior
vanish, respectively. The OIE's on T_g and T_N are found to have {\it opposite
signs} as compared to the OIE on T_c. All OIE's are suggested to arise from the
isotope dependent mobility (kinetic energy) of the charge carriers.
