Structure of the Glycyl-L-histidyl-L-lysine--copper(II) complex in solution.
Freedman. J H JH; Pickart. L L; Weinstein. B B; Mims. W B WB; Peisach. J J
Key Findings
- At neutral (physiological) pH, GHK‑Cu exists as a mononuclear 1:1 complex, not as polymeric clusters.
- Copper coordination involves nitrogen atoms, with the histidine imidazole ring providing a key binding site.
- Three pH‑dependent transitions were identified (pK ≈ 3.6, 9.2, 11.4), indicating changes in protonation but the core Cu‑histidine bond remains intact even at higher pH.
- The solid‑state polymeric structure reported in older X‑ray studies does not represent the peptide’s behavior in solution.
Practical Outcomes
- For supplement makers and DIY users, this means GHK‑Cu is stable as a single‑copper complex at the pH of blood and skin, supporting its use in topical or oral formulations. Formulations should avoid extreme alkaline conditions that could alter the complex’s shape, though the copper will still stay attached. Storage in neutral‑pH solutions is likely to preserve the intended structure and activity.
Summary
The study shows that the GHK‑Cu peptide forms a single‑copper (1:1) complex in water at the pH found in the body. The copper is attached mainly to nitrogen atoms, especially the histidine part of the peptide. At higher pH the shape of the complex shifts a little, but the copper stays bound. The solid‑state crystal form that looks like copper pairs linked by oxygen does not exist in solution.
Abstract
Optical, electron paramagnetic resonance, and electron spin-echo envelope spectroscopies were used to examine the structure of the Cu(II) complex of glycyl-L-histidyl-L-lysine (GHL) in solution. At neutral pH, GHL forms a mononuclear 1:1 Cu(II) compound having an EPR spectrum resembling that of Cu(II) equatorially coordinated by two or three nitrogen atoms. Electron spin-echo studies demonstrate that one of these is located in the histidyl imidazole ring. A pH titration of Cu(II)-GHL shows three optical transitions with apparent pKs of 3.6, 9.2 and 11.4 and molecularities, with respect to protons, of 2, 2, and 1, respectively. At the lowest pK, GHL binds Cu(II), forming the species present at physiological pH. At elevated pH, spectroscopic experiments suggest that an alteration of the Cu(II) structure occurs, yet the bound imidazole is retained. These solution studies are consistent with nitrogen coordination of Cu(II) in Cu(II)-GHL, but the solid-state polymeric structure, with oxygen-bridged Cu(II) pairs as previously determined by X-ray crystallographic analysis [Pickart, L., Freedman, J. H., Loker, W. J., Peisach, J., Perkins, C. M., Steinkamp, R. E., & Weinstein, B. (1980) Nature (London) 288, 715-717; C. M. Perkins, N. J. Rose, R. E. Steinkamp, L. H. Jensen, B. Weinstein, and L. Pickart, unpublished results], does not exist in solution.
Study Information
pubmed
1982
1982-09-14T00:00:00.000Z
10.1021/bi00262a004