Human serum albumin complexes with chlorophyll and chlorophyllin

Abstract

Porphyrins and their metal derivatives are strong protein binders. Some of these compounds have been used for radiation sensitization therapy of cancer and are targeted to interact with cellular DNA and protein. The presence of several high-affinity binding sites on human serum albumin (HSA) makes it possible target for many organic and inorganic molecules. Chlorophyll a and chlorophyllin (a food-grade derivative of chlorophyll), the ubiquitous green plant pigment widely consumed by humans, are potent inhibitors of experimental carcinogenesis and interact with protein and DNA in many ways. This study was designed to examine the interaction of HSA with chlorophyll (Chl) and chlorophyllin (Chln) in aqueous solution at physiological conditions. Fourier transform infrared, UV-visible, and CD spectroscopic methods were used to determine the pigment binding mode, the binding constant, and the effects of porphyrin complexation on protein secondary structure. Spectroscopic results showed that chlorophyll and chlorophyllin are located along the polypeptide chains with no specific interaction. Stronger protein association was observed for Chl than for Chln, with overall binding constants of K(Chl) = 2.9 x 10(4)M(-1) and K(Chln) = 7.0 x 10(3)M(-1). The protein conformation was altered (infrared data) with reduction of alpha-helix from 55% (free HSA) to 41-40% and increase of beta-structure from 22% (free HSA) to 29-35% in the pigment-protein complexes. Using the CDSSTR program (CD data) also showed major reduction of alpha-helix from 66% (free HSA) to 58 and 55% upon complexation with Chl and Chln, respectively.

<b>Synthesis and DNA interaction of a Sm(III) complex of a Schiff base derived from vanillin and L-tryptophan</b>

“…The binding constant of Sm(III)L with DNA was determined using the following relationship [22][23]: . The thermodynamic parameters show the binding mode [24].…”

Study on the Interactions of Kaempferol and Quercetin with Intravenous Immunoglobulin by Fluorescence Quenching, Fourier Transformation Infrared Spectroscopy and Circular Dichroism Spectroscopy

“…28,29) It is inferred that IgG probably has more potential binding sites for antigens/ semi-antigens. 30) Figure 4 and Table 1 show that the Sips plots display better linear correlations whether the number of binding sites (n) is 2 or 4, and both of the affinity constants present at the order of magnitude about 10 4 M Ϫ1 , indicating that they are of non-specific and weak interactions with respect to the other strong ligand-protein complexes with the binding constants ranging from 10 6 to 10 8 M Ϫ1 , 31) and that the binding sites of IVIG for the two drugs are probably the two antigen-binding fragments (Fab) and the two crystallizable fragments (complement-binding sites, Fc).…”

Spectroscopic studies on the interaction between tryptophan–erbium(III) complex and herring sperm DNA

“…The absorption relationship between the complex and DNA was expressed by double reciprocal equation [14]:…”