LHRH interaction with Zn(II) ions

Zn2+-triggered self-assembly of Gonadorelin [6-D-Phe] to produce nanostructures and fibrils

A synthetic derivative, GnRH [6-D-Phe], stable against enzymatic degradation, self-assembles and forms nanostructures and fibrils upon a pH shift in the presence of different concentrations of Zn²⁺in vitro. Attenuated Total Reflection Fourier Transform Infrared spectroscopy (ATR–FTIR) revealed the existence of higher order assembly of Zn²⁺: GnRH [6-D-Phe]. Nuclear Magnetic Resonance spectroscopy (NMR) indicated a weak interaction between Zn²⁺ and GnRH [6-D-Phe]. Atomic Force Microscopy (AFM) showed the existence of GnRH [6-D-Phe] oligomers and fibrils. Molecular Dynamic (MD) simulation of the 10:1 Zn²⁺: GnRH [6-D-Phe] explored the interaction and dimerization processes. In contrast to already existing short peptide fibrils, GnRH [6-D-Phe] nanostructures and fibrils form in a Tris-buffered pH environment in a controlled manner through a temperature reduction and a pH shift. The lyophilized Zn²⁺: GnRH [6-D-Phe] assembly was tested as a platform for the sustained delivery of GnRH [6-D-Phe] and incorporated into two different oil vehicle matrices. The in vitro release was slow and continuous over 14 days and not influenced by the oil matrix.

Preparation and properties of selected Zn(II)–peptide complexes in suspension

The preparation and properties of low soluble, suspended Zn(II) complexes containing the selected peptides: tyroliberin (TRH), gonadorelin (GnRH), dalarelin and corticothropin (ACTH) were studied. The amount of Zn(II) bound by 1 muM of the selected peptide (n) was defined, as well as affinity of Zn(II) to the peptide (Ka) and the durability of the created complex Zn(II)-peptide (Kd). ACTH associated the highest amount of Zn(II), and GnRH the lowest one: 1 microM of ACTH complexed 0.81 microM +/- 0.03 Zn(II), the same quantity of GnRH-0.52 microM +/- 0.07 and TRH and dalarelin associated 0.75+/-0.03 and 0.79+/-0.02 microM of Zn(II), respectively. The closest affinity was stated between Zn(II) and GnRH (Ka=157.692+/-21.300 microM(-1)), the smallest-towards ACTH (Ka=1.136+/-0.042 microM(-1)). The lower amount of Zn(II) associated by the studied peptide, the higher was its affinity versus this metal (r=-0.942). The analysis of the kinetics of the Zn(II)-peptide linkage revealed that the most stable complexes with this metal were formed by GnRH (Kd=0.006+/-0.001 microM(-1)) and by dalarelin (Kd=0.020+/-0.001 microM(-1)). Zn(II) with GnRH complexes are about 147 times more durable than ACTH (Kd=0.880+/-0.033 microM(-1)) ones. It was established that the Zn(II)-peptide complexes were more stable in the case of lower molecular weight of the peptide (r=0.963), and the inferior number of the amino acid residues accessible in the peptide (r=0.967).

Ovulation-inducing activity of luliberin (LHRH) complexed by copper(II), nickel(II), and zinc(II) ions

We have shown that the complexation of luteinizing hormone releasing hormone, luliberin (LHRH), a hypothalamic neurohormone, by Cu(II), Ni(II), and Zn(II) may affect its basic, ovulation-inducing potency in the dose responsive manner. Some explanation of the obtained results are offered here.