believe that the precise definition of the coordinate geometry of copper a t the active site will be crucial to understanding its functional operation. Also, the subtle changes t h a t allow t h e dinuclear site to become catalytically active in, for example, tyrosinase and laccase'1*42-44 will also be an interesting outcome of gaining a more precise definition of t h e active-site structure of hemocyanin a n d its related binuclear copper proteins.45
42)Karlin, K. D.; Gultneh, Y. Prog. Inorg. Chem. 1987, 35, 219. 43) Latour, J.-M. Bull. SOC. Chim. Fr. 1988, 508. 44) Sorrell, T. N. Tetrahedron 1989, 45, 3. 45) The structure of the multicopper-containing enzyme ascorbate oxidase has just appeared: Messerschmidt, A.; Rmi, A.; Ladenstein, R.; Huber, R.; Bolognesi, M.; Gatti, G.; Marchesini; Petruzzelli, R.; Finazzi-Agrb, A. J . Mol. Biol. 1989, 206, 513. 124021-05-2; 5, 124021-07-4; [ C U ( M~C N )~] C F~S O , , 58452-28-1; [Cu-(MeCN)4]C104, 14057-91-1; [Cu( MeCN),]BF4, 1541 8-29-8.
Supplementary Material Available:Tables S1, S4, S7, and SI0 (anisotropic thermal parameters), Tables S2, S5, S8, and SI 1 (bond distances), and Tables S3, S6, S9, and S12 (bond angles) for compounds 1-4, respectively (15 pages). Ordering information is given on any current masthead page.The binding of aluminum to human serum transferrin in 0. IO M N-(2-hydroxyethyl)piperazine-N'-ethanesulfonic acid and 5 mM sodium bicarbonate at pH 7.4 has been studied by difference ultraviolet spectrophotometry. Aluminum binding produces peaks at 240 and 288 nm that are characteristic of binding at the transferrin specific metal binding sites. The more intense peak at 240 nm has a molar absorptivity of 14 800 f 1600 M-' cm-l and has been used to determine two macroscopic aluminum binding constants of log KI* = 13.5 & 0.2 and log K2* = 12.5 f 0.3. Titrations of both forms of monoferric transferrin with AI3+ indicate that the larger K I * value is associated primarily with AI binding at the C-terminal site and the smaller K2* value is associated primarily with the N-terminal site. The AI-transferrin binding constants have been used to include transferrin in the equilibrium distribution of aluminum calculated by using a computer model of serum. This model has been used to evaluate the potential of several low molecular weight ligands for use in decorporation of aluminum. Sciences Research Support Grant No. 2S07RR07170-11 at the University of Idaho. We wish to thank Dr. A. E. Martell for helpful discussions and for providing preprints of ref 37 and 54.Registry No. EXAFS spectroscopy has been applied to investigate the nature and the stereochemistry of the iron(II1) binding sites in the protein phosvitin from chicken eggs in water solution with an iron/protein molar ratio of 10/1 at pH 7.2. The main result is that the iron atoms are bound to the protein in an octahedral environment and that the main binding sites are provided by the oxygen atoms of serine-bound phosphate groups at 1.93 (2) A from the metal. The average number of bound phosphate groups is 4.4...