Valinomycin and its interaction with ions in organic solvents, detergents, and lipids studied by Fourier transform IR spectroscopy

Abstract

The structure of valinomycin in a range of organic solvents of varying polarity and in detergent and lipid dispersions has been studied by Fourier transform ir spectroscopy. In solvents of low polarity such as chloroform, ir spectra of valinomycin are fully consistent with the bracelet structure proposed on the basis of nmr spectroscopy, showing a single narrow amide I component attributable to the presence of beta-turns and a single band arising from nonhydrogen-bonded ester C = O groups. K+ complexation results in a downward shift in the amide I band frequency, indicating an increase in the strength of the amide hydrogen bonds, along with a shift to lower frequencies of the ester C = O absorption due to a reduction in electron density in these bonds upon complexation. Identical results were obtained with NH4+, a finding not previously reported. In solvents of both medium (CHCl3/DMSO 3:1) and high (pure DMSO) polarity, we find evidence of significant disruption of the internal hydrogen-bonding network of the peptide and the appearance of a band suggesting the presence of free amide C = O groups. In such solvents, complexation with K+ and NH4+ was not observed. The structure of valinomycin in detergent micelles resembles that in nonpolar organic solvents. However, changes were found in the amide I and ester carbonyl maxima as 2H2O penetrated the micelle which suggest significant interaction between the solvent and peptide. Complexation with K+ was reduced in cationic detergent micelles as a result of a decrease in the effective K+ concentration due to charge repulsion at the micelle surface.(ABSTRACT TRUNCATED AT 250 WORDS)

New Fourier transform infrared based computational method for peptide secondary structure determination. II. Application to study of peptide fragments reproducing processing site of ocytocin–neurophysin precursor

“…The FTIR spectra of peptides XXIII and [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] before (XXIII H , [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] H ) and after deuteration (XXIII D , [1][2][3][4][5][6][7][8][9][10][11][12][13]…”

“…The related Fourier self-deconvolution (FSD), second derivative (2ndD), and 4thD curves (A H -C H and A D -C D ) are reported in Figure 2 (XXIII) and ). It should be noted that, only the figures concerning peptides XXIII and [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] are presented here, although similar measurements were performed on all peptides listed in Table I. The application of BN methods to all peptides, after subtraction of the H 2 O or D 2 O baseline spectra, is summarized in Table II. Peptide XXIII presented amide I components at wave numbers close to those found for XXIV, including the minor components below 1650 cm Ϫ1 .…”

“…Peptide [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] instead showed shifted low wave number components located at 1648 -1637, 1630 -1625, 1616 -1612, and 1596 -1577 cm Ϫ1 . In peptides XXIII, [Pro 7 ]-XXIII, and [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] the FSD allowed the resolution of a new band located at around 1720 cm Ϫ1 (H 1 3 D 1 ), which was attributed to the side chain ␤-carboxylic function of the Asp residues. 12,13 The most significant absorptions for all the peptides, which were located at 1695-1688 (H 2 3 D 2 or D 1 ), 1685-1679 (H 3 3 D 3 or D 2 ), 1672-1664 (H 4 3 D 4 or D 3 ), and 1661-1654 cm Ϫ1 (H 5 D 5 or D 4 ), were not affected by concentration.…”

Direct binding of halide ions by valinomycin

“…It is an antibiotic produced by Streptomyces fulvissimus and is a dodecadepsipeptide composed of three identical fragments that form a 36-member macrocycle (Figure 1). Valinomycin binds to alkali (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15), alkaline earth (7,12,16), transition metal (12,17) and ammonium ions (8) in solution. It is highly selective for potassium ions over sodium ions in solution, and its function as an antibiotic is based on selective transport of potassium over sodium ions across biological membranes (1,2).…”

“…It is highly selective for potassium ions over sodium ions in solution, and its function as an antibiotic is based on selective transport of potassium over sodium ions across biological membranes (1,2). The interaction between valinomycin and metal ions (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17), in particular alkali metal ions (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15), has been studied extensively by a variety of experimental techniques, including NMR (3-6, 11, 15, 16), infrared (IR) (6,8,11,17), circular dichroism (CD) (15,17) and Raman (7,13) spectroscopy as well as mass spectrometry (9,10,12). In recent years, computational studies (18) pertaining to the binding of valinomycin to cations have also been reported.…”