Stopped-Flow Spectroscopic Studies on the Ligand-Exchange Reaction of Cu–(Glycine-Peptide) Complexes, Cu(H−iL), with Cysteine. Cu(II) Transport and Characterization of the Intermediate Ternary Complexes Cu(H−1L)(Cys−); L = Glycylglycine (i = 1), Triglycine (i = 2), Tetraglycine (i = 2 or 3), and Pentaglycine (i = 2 or 3)

Abstract

Cu(II) complexes of glycine-peptides, abbreviated as Cu(H−iL): L = glycylglycine, triglycine, tetraglycine, and pentaglycine (i = 1–3), react with cysteine to form ternary complexes, Cu(H−1L)(Cys−), as first intermediates. The spectral parameters of the ternary complexes, which were similar irrespective of the peptides, were as follows: λmax = 332 ± 1 nm (ε = 4250 ± 50 M−1 cm−1), g|| = 2.170 ± 0.005, g⊥ = 2.00 ± 0.05, and A|| = (2.05 ± 0.01) × 10−4 cm−1, indicating that the ternary complexes have identical coordination structures: the Cu(II) coordinates with the peptides via the nitrogens from the terminal amino and the neighboring deprotonated-amide group, and with cysteine via the amino nitrogen and the thiolate sulfur. Based on the absorbance-time curves, the concentrations of each Cu(II) and Cu(I) species during the reaction were calculated. The species distribution curve clearly visualized the pathway of the Cu(II) transport from Cu(H−iL) to Cu(Cys−)2 via Cu(H−1L)(Cys−). The rate of Cu(H−1L)(Cys−) formation, which was evaluated from the initial increase in the species distribution curve, depended on the coordination modes of the Cu(H−iL) complexes. Both the Cu(H−1L), involving N,N−,O−,O* donors, and the Cu(H−2L), involving N,N−,N−,O−* donors, rapidly formed Cu(H−1L)(Cys−) complexes, where the donors asterisked represent the fourth ligand in the Cu(H−iL) complexes. The second-order rate constant, k1+, was on the order of 106 M−1 s−1, or bigger. The Cu(H−3L), involving N,N−,N−,N−* donors, reacted relatively slowly; k1+ was on the order of 104 M−1 s−1. Those results indicate that the affinity of the Cu(II) for the fourth donor in Cu(H−iL) determines the rate of metal-transport.

Demonstration of the Importance of Metal Ion Speciation in Bioactive Systems

“…I. Sóvágó (University of Debrecen, Hungary) for the valuable discussion and comments on the . Time-dependent distribution of the copper species formed in the reactions of Cu(H À2 GlyGlyHis) (above) 83 and Cu(H À2 GlyGlyGly)(below) 84 with Cys at pH 8.7.…”

Transport of Cu(II) from an albumin mimic peptide, GlyGlyHisGly, to histidine and penicillamine

“…The absorption spectrum of the transient was prepared by a point-by-point method plotting the absorbance against the wavelength [17]. The species distribution relative to the reaction time was calculated by the method reported previously [17].…”

“…The species distribution relative to the reaction time was calculated by the method reported previously [17]. The dead time (DT) of the instrument determined by the reaction of ascorbate with 2,4-dichlorophenolindophenol was 1.2 ms [21].…”

“…To obtain the detailed mechanism we have been investigating the dynamics and statics of the reaction between Cu(II)-glycine peptide complex, Cu(H Ài L) (i = 1, 2, or 3) and Cysteine (Cys), where L denotes the anionic peptide and i means the ith deprotonation of the amide moiety due to the Cu-N bond formation [17]. In addition aminothiol (Rs) such as Cys and penicillamine (Pes) were useful for proving the existence of short-lived intermediate Cu(II) complexes such as Cu(H À1 L)(Rs À ) and Cu(Rs À ) 2 , because these intermediates exhibited the intense S À !…”

“…The fourth donor in Cu(H À3 G5) is the deprotonated amide nitrogen of the third peptide bond, while the fourth-donor in Cu(H À2 GGHG) is the imidazole nitrogen of His. The transport of Cu(II) in Cu(H Ài L) is triggered off by the ligand replacement in the fourth-binding site [17], so that the nature of the fourth-donor in Cu(H Ài L) is important in deciding the easiness of the ternary complex formation.…”