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The temperature and frequency dependence of the 19F NMR spin-spin (1/T2) and spin-lattice (l/7\) relaxation rates of F~in the presence of the copper-containing enzyme galactose oxidase have been analyzed. The magnitudes of the dipolar and scalar electron-nuclear interactions obtained from this analysis are both about four times smaller than those which have been determined previously for aqueous CuF+. The major contribution to the dipolar relaxation mechanism comes from unpaired electron spin in p orbitals centered at the bound F"; no more than 38% is due to the point-dipole interaction between the 19F nucleus and unpaired electron spin centered at the enzyme Cu(II). Pseudothermodynamic parameters for the binding of F" to the enzyme Cu(II) site were determined: K{ = 6.9 X 10~2 M"1 at 50 °C, AH0 = -4.2 X 101 kJ mol"1. The smaller values for these superhyperfine and binding constants, compared to those for aqueous CuF+, are consistent with axial, rather than equatorial coordination to the Cu(II) of the F detected

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