Electrostatic properties of myoglobin probed by diffusion-enhanced energy transfer

The use of lanthanide energy transfer in the "rapid-diffusion limit" for probing the electrostatic properties of proteins has been investigated by measuring rates of energy transfer from Tb(III) chelates (having charges 1+, 0, and 1-) to the heme of sperm whale met(aquo)myoglobin, as a function of pH. The results are in good agreement with the predictions of a simple model involving the overall charge of the protein. The preparation of terbium(III) N,N′-bis(2-hydroxyethyl)-ethylenediaminediacetate, a new positively charged Tb(III) chelate similar in size and shape to negative terbium(III) ethylenediaminetetraacetate and neutral terbium(III) N-(2-hydroxyethyl)ethylenediaminetriacetate, is described.