Interaction and coordination geometries for Ag(I) in the two metal sites of hemocyanin

Abstract

111 Ag(I) perturbed angular correlations of g-rays (PAC) has been used to investigate the binuclear metal site of 111 Ag(I)-substituted Carcinus aestuarii deoxyhemocyanin. The studies have shown that apo-hemocyanin is able to bind 2 mol of Ag(I) per mol of protein and that the binding is specific for the metal ion sites. The PAC spectra show pronounced changes when the stoichiometry of Ag(I) to protein is increased from 0.1 to 2.0. These changes have been interpreted as evidence of interactions between the two sites in terms of a structural destabilization of the first occupied site caused by the occupation of the second site. The experimental data for the Ag(I)-substituted metal sites do not agree well with the three-coordinated structure found in the Cu(I) holo-protein. However, if a water molecule is included as a coordinating ligand in the Ag(I) metal site a successful interpretation of the experimental data can be obtained.

Periplasmic Metal-Resistance Protein CusF Exhibits High Affinity and Specificity for Both CuI and AgI

“…However, the two ions do not necessarily behave the same in all cases (40). For example, in hemocyanin, Ag I takes an extra water ligand as compared to Cu I , and Cox17, the copper chaperone for cytochrome c oxidase, binds Cu I with high affinity but does not bind Ag I at all (41,42). In the case of Cox17, which has a multinucleate CuS cluster, the authors suggest that the preference for a particular ion may be due to the size difference between copper and silver.…”

Probing the Bioinorganic Chemistry of Cu(I) with 111Ag Perturbed Angular Correlation (PAC) Spectroscopy

“…Ag(I), and consequently that the binding of the two metal ions is likely to be cooperative. The binuclear Cu site in deoxy-Hc from the arthropod Carcinus aestuarii was charac terized by 111 Ag PAC spectroscopy by Holm et al [30] through a series of experiments with varying Ag(I)-to-protein ratios. Note that the amount of radioactive 111 Ag is very small, so the Ag(I) concentration is controlled by the addition of non-radioactive Ag(I) typically as a nitrate or perchlorate salt.…”

“…It was concluded that purely three-coordinated Ag(I) does not agree well with the 111 Ag PAC spectroscopic data, and that it is likely that a fourth ligand, for example, a water molecule, may be pre sent both with one and with two Ag(I) bound to Hc. In the work by Holm et al [30], it was assumed that the local Ag(I) metal site structure persisted throughout the PAC measure ments, i.e., that little or no structural relaxation occurred, despite the change of elemen and oxidation state accompanying the nuclear decay of 111 Ag(I) to 111 Cd(II). Later experi ments on the CueR transcriptional regulator [32], vide infra, have demonstrated that this assumption may not always hold.…”

“…Later experi ments on the CueR transcriptional regulator [32], vide infra, have demonstrated that this assumption may not always hold. Therefore, it is conceivable that the conclusion of the The structural interpretation of the recorded PAC signals was carried out by Holm et al [30] using the semiempirical angular overlap model (AOM) [40]. It was concluded that purely three-coordinated Ag(I) does not agree well with the 111 Ag PAC spectroscopic data, and that it is likely that a fourth ligand, for example, a water molecule, may be present both with one and with two Ag(I) bound to Hc.…”

“…With this work, we review applications of 111 Ag PAC spectroscopy within Cu(I) bioinorganic chemistry, which so far only encompasses electron transfer proteins (plastocyanin and azurin) [26][27][28][29], an oxygen transport protein (hemocyanin) [30], and metal-ionsensing proteins functioning as transcriptional regulators (CueR and BxmR) [31][32][33].…”