Spin-density distribution in the copper site of azurin.

A 95 GHz pulsed deuterium ENDOR study has been performed on single crystals of azurin from Pseudomonas aeruginosa selectively deuterated at the C(beta) position of the copper-coordinating cysteine 112. Complete hyperfine tensors of the two deuterium atoms have been obtained, which reveal identical isotropic parts. Analysis of the hyperfine tensors provides insight into the spin-density delocalization over the cysteine ligand. Approximately 45 % of the spin density in the paramagnetic site can be attributed to copper and 30 % to sulfur.