Interaction of Small Zinc Complexes with Globular Proteins and Free Tryptophan

Abstract

A series of eight water soluble anionic, cationic, and neutral zinc(II) complexes were synthesized and characterized. The interaction of these complexes with bovine serum albumin (BSA), human serum albumin (HSA), lysozyme, and free tryptophan (Trp) was investigated using steady-state fluorescence spectroscopy. Static and dynamic fluorescence quenching analysis based on Stern-Volmer kinetics was conducted, and the decrease in fluorescence intensity of the Trp residue(s) can be ascribed predominantly to static quenching that occurs when the Zn complex binds to the protein and forms a nonfluorescent complex. The role played by the nature of the ligand, the metal, and complex charge in quenching Trp fluorescence was investigated. The binding association constants (Ka) ranged from 104 to 1010 M−1 and indicate that complexes with planar aromatic features have the strongest affinity for globular proteins and free Trp. Complexes with nonaromatic features failed to interact with these proteins at or in the vicinity of the Trp residues. These interactions were studied over a range of temperatures, and binding was found to weaken with the increase in temperature and was exothermic with a negative change in entropy. The thermodynamic parameters suggest that binding of Zn complexes to the proteins is a highly spontaneous and favorable process.

Ageing, dehulling and cooking of Bambara groundnuts: consequences for mineral retention and in vitro bioaccessibility

“…52 For instance, the bioaccessibility of Zn in chickpeas and cowpeas decreased by 11% and 63%, respectively, after microwave cooking. 53 According to the study on chickpeas and cowpeas, the decrease in Zn bioaccessibility due to cooking time was attributed to the complexation of Zn with proteins. As whole legumes are cooked, both the starch and proteins become enclosed within the cell walls.…”

Supramolecular interaction of transition metal complexes with albumins and DNA: Spectroscopic methods of estimation of binding parameters

“…The major attention in the case of metal complexes binding with proteins is paid to the therapeutic properties, and only in some cases the binding parameters were studied which, if necessary, were improved by changing temperature [8,23,[33][34][35][36][37][38][39] or selecting organic and inorganic coligands (mostly 1,10-phenantholine and bipyridyl) which bind with a complexing metal together with a drug molecule. [8,24,36,37,[39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54] The complexes under study are mainly biligand complexes containing a drug ligand and coligand. The Figure 3 shows the distribution of the studing from the viewpoint of metals studied.…”

“…As the result, the study of their interaction with serum albumins is extremely important. [130] BSA has a structure similar to human serum albumin (its sequence is 76% identical to HSA), [53] though significantly different from it from the fluorimetric properties. A BSA macromolecule consists of 582 amino acid residues, including 20 tyrosine residues and, unlike in HSA, two tryptophan residues, one of which is situated at the protein surface (Trp134), and the other one is located nearer to the inner part (Trp212).…”

“…[131] BSA, as well as HSA, performs the delivery function for many compounds. [53] Tryptophan, tyrosine, and phenylalanine residues are the pivotal fluorescent groups in albumins. Tryptophan is a prevailing fluorescent component in most proteins.…”

Cation-induced shape programming and morphing in protein-based hydrogels

“…It is also well known that BSA can bind cations at various exposed amino acids (23,24). For example, divalent cations such as Ni 2+ , Cu 2+ , and Zn 2+ were shown to bind histidine (25,26) and tryptophan (24), and to bridge cysteine amino acids (27). Adsorption of cations was also associated with an increase in the mechanical stability of proteins at the molecular level (28,29).…”