Hemoglobin−Silver Interaction and Bioconjugate Formation: A Spectroscopic Study

Abstract

In this article, we report the results of the extent of interaction as well as the formation of a bioconjugate of human hemoglobin (Hb) with silver (Ag). The complexation process and conformational changes are characterized using different spectroscopic and microscopic techniques. The UV-vis study demonstrates the perturbation of the soret/heme band and generates conformational heterogeneity within the heme group in the presence of silver. A fluorescence study suggests that the Tryptophan (Trp) residues of Hb are in a more polar environment after conjugation. Initial fluorescence enhancement with addition of silver is due to metal-enhanced fluorescence. Moreover, the fluorescence quenching after the formation of the Hb-Ag bioconjugate follows the modified Stern-Volmer (S-V) plot. The S-V plot along with the time-resolved fluorescence study indicates the presence of both static and dynamic types of quenching. In addition, the reduction potential values of the entities (Hb-heme, Ag(+), and Trp) indicate the possible electron transfer. The secondary structure calculation from CD and FTIR spectra indicate alpha-helix to beta-sheet conversion, and unfolding of Hb is also responsible for the bioconjugate formation. In addition, FE-SEM, phase contrast inverted microscopy (PCIM) images demonstrate the formation of the silver-protein bioconjugate. The overall data show that there is a change in the secondary as well as the tertiary structure of Hb after conjugation with silver.

Interaction of cyanidin-3-O-glucoside with three proteins

“…In addition, the peak at about 410 nm is called the Soret band and is the characteristic peak of heme proteins, which can be attributed to the electronic transition of p ? p ⁄ of hematoporphy in Hb or Mb (Mahato et al, 2010). The spectral changes of these peaks can reflect the polypeptide backbone structural change, the microenvironment of aromatic acid residues of proteins, or the conformational change near the heme moiety in Hb or Mb.…”

“…Proteins are important biomacromolecules that play various roles in living beings (Mahato et al, 2010). Serum albumin is the most abundant drug carrier protein in blood plasma, which has many physiological functions, such as maintaining the osmotic pressure and pH of blood, and as carriers transporting a great number of endogenous and exogenous compounds such as fatty acids, amino acids, drugs and pharmaceuticals (Kratz, 2008).…”

Binding of fluorescent acridine dyes acridine orange and 9-aminoacridine to hemoglobin: Elucidation of their molecular recognition by spectroscopy, calorimetry and molecular modeling techniques

“…2A). The former peak is primarily due to the π-π* transition of the carbonyl (C_O) groups of the amino acid residues, while the latter is the porphyrinSoret band or B band (π-π* transition) which originates from the heme moiety embedded in the hydrophobic pocket formed by the protein's backbone through appropriate folding [35].…”

Binding studies of hydroxylated Multi-Walled Carbon Nanotubes to hemoglobin, gamma globulin and transferrin

“…Then the second absorption peak in the region 250-300 nm arises from the transition of ᴨ → ᴨ* of phenyl groups in tryptophan (Trp), tyrosine (Tyr) and phenylalanine (Phe) in Hb [43]. In addition, the third peak at about 410 nm is called the soret band and is the characteristic peak of heme proteins, which belongs to the electronic transition of ᴨ → ᴨ * of hematoporphyrin in Hb [44]. The spectral changes of these three peaks can reflect the polypeptide backbone structural change, the microenvironment of aromatic acid residues, and the conformational change near heme moiety in Hb, respectively.…”