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PubMed1988

The secondary structure of apolipoproteins in human HDL3 particles after chemical modification of their tyrosine, lysine, cysteine or arginine residues. A Fourier transform infrared spectroscopy study.

Fourier transform infrared spectra of apolipoprotein E-depleted human HDL3 have been obtained in H2O and 2H2O buffers. The absorption bands in the protein amide I and amide II regions (1700-1500 cm-1) were assigned to alpha-helical, disordered and beta-strand/beta-turn structures of apolipoproteins A-I and A-II (apoA-I and apoA-II), the apolipoprotein constituents of HDL3. Modification of HDL3 by tetranitromethane (TNM) treatment, acetylation, reduction plus alkylation and 1,2-cyclohexanedione treatment derivatised tyrosine, lysine, cysteine and arginine residues, respectively, and caused alteration of the secondary structure of the HDL3 apolipoproteins to different extents. Each of the chemical modifications caused changes in the frequency of bands associated with beta-strands/beta-turns, but only TNM treatment of HDL3, as judged by the second- and fourth-derivative spectra, resulted in a shift of the band assigned to the alpha-helical structure of the proteins. In agreement with other workers, only TNM treatment of HDL3 particles was found to inhibit their binding by high-affinity cell membrane receptors. It is proposed, therefore, that receptor recognition of HDL3 particles is dependent on conservation of the alpha-helix structures within apoA-I and apoA-II, and that beta-strand/beta-turn structures are not involved. This conclusion is consistent with the predominance of amphipathic alpha-helical structures in both apolipoproteins and with the relaxed specificity of the receptors which are thought to recognise both apoA-I and apoA-II.

Acylation↗

PubMed1992

Water structural changes in the bacteriorhodopsin photocycle: analysis by Fourier transform infrared spectroscopy.

The Fourier transform infrared difference spectra between light-adapted bacteriorhodopsin (BR) and its photointermediates, L and M, were analyzed for the 3750-3450-cm-1 region. The O-H stretching vibrational bands were identified from spectra upon substitution with 2H2O. Among them, the 3642-cm-1 band of BR was assigned to water by substitution with H2(18)O. By a comparison with the published infrared spectra of the water in model systems [Mohr, S.C., Wilk, W.D., & Barrow, G.M. (1965) J. Am. Chem. Soc. 87, 3048-3052], it is shown that the O-H bonds of the water in BR interact very weakly. Upon formation of L, the interaction becomes stronger. The O-H bonds of the protein side chain undergo similar changes. On the other hand, M formation further weakens the interaction of the same water molecules in BR. The appearance of a sharp band at 3486 cm-1, which was assigned tentatively to the N-H stretching vibration of the peptide bond, is unique to L. The results suggest that the water molecules are involved in the perturbation of Asp-96 in the L intermediate and that they are exerted from the protonated Schiff base which changes position upon the light-induced reaction.

Bacteriorhodopsins↗

PubMed2005

Unfolding features of bovine testicular hyaluronidase studied by fluorescence spectroscopy and fourier transformed infrared spectroscopy.

Chemical unfolding of bovine testicular hyaluronidase (HAase) has been studied by fluorescence spectroscopy and Fourier transformed infrared spectroscopy (FTIR). Thermodynamic parameters were determined for unfolding HAase from changes in the intrinsic fluorescence emission intensity and the formations of several possible unfolding intermediates have been identified. This was further confirmed by representation of fluorescence data in terms of 'phase diagram'. The secondary structures of HAase have been assigned and semiquantitatively estimated from the FTIR. The occurrence of conformational change during chemical unfolding as judged by fluorescence and FTIR spectroscopy indicated that the unfolding of HAase may not follow the typical two-state model.

Animals↗

PubMed2005

Detection of sugar adulterants in apple juice using fourier transform infrared spectroscopy and chemometrics.

Fourier transform infrared spectroscopy and attenuated total reflection sampling have been used to detect adulteration of single strength apple juice samples. The sample set comprised 224 authentic apple juices and 480 adulterated samples. Adulterants used included partially inverted cane syrup (PICS), beet sucrose (BS), high fructose corn syrup (HFCS), and a synthetic solution of fructose, glucose, and sucrose (FGS). Adulteration was carried out on individual apple juice samples at levels of 10, 20, 30, and 40% w/w. Spectral data were compressed by principal component analysis and analyzed using k-nearest neighbors and partial least squares regression techniques. Prediction results for the best classification models achieved an overall (authentic plus adulterated) correct classification rate of 96.5, 93.9, 92.2, and 82.4% for PICS, BS, HFCS, and FGS adulterants, respectively. This method shows promise as a rapid screening technique for the detection of a broad range of potential adulterants in apple juice.

Beverages↗

PubMed1994

Erythrocyte peroxidation: quantitation by Fourier transform infrared spectroscopy.

We used Fourier transform infrared spectroscopy (FT-IR) to quantitatively monitor peroxidative damage in model phospholipids and in human erythrocyte membranes. The 3012-cm-1 band arising from olefinic C-H stretching modes diminished in intensity during membrane peroxidation as a result of loss of unsaturation in the phospholipid acyl chains. A precise (correlation coefficient = 0.99) linear relationship between the number of C = C bonds in the chains and the fraction of the total C-H stretching contour occupied by the olefinic C-H stretch was established for model phospholipids. Intact human erythrocytes and isolated ("ghost") membranes were also peroxidized and the loss of C = C bonds was demonstrated by FT-IR. GC studies of erythrocyte membranes confirmed that the primary site of peroxidation occurred at phospholipids containing arachidonate acyl chains. Finally, the formation of a new feature at 1260 cm-1 in the FT-IR spectrum was observed in both model compounds and erythrocyte membranes undergoing peroxidative damage. The feature corresponds to a C-O stretching and/or O-H in-plane bending vibration and is suggestive of the formation of these functional groups during peroxidation. FT-IR provides an accurate means for monitoring the effects of peroxidative damage in human erythrocytes.

Erythrocyte Membrane↗

PubMed2001

Study on the secondary structure of protein in amide I band from human colon cancer tissue by Fourier-transform infrared spectroscopy.

BACKGROUND: Fourier-transform infrared spectroscopy (FT-IR) is a powerful tool for study of the secondary conformation of intact protein in biological tissues and for diagnosis of disease states. The purpose of this study is to utilize FT-IR as a diagnostic tool to estimate the secondary structure of amide I in normal and cancer tissue of human colon. METHODS: Pairs of tissue samples from colon cancer and histologically normal mucosa tissue 5-10 cm from the tumor were obtained from a patient who underwent partial colectomy. In the present study we investigated the changes in the secondary structure of amide I of normal and malignant human colon tissue using FT-IR microspectroscopy with attenuated total reflectance. Secondary-derivative analysis relative to the original and curve-fitting analysis infrared spectra were also carried out. RESULTS: The conformational changes of the secondary structure of protein in normal and cancerous human colon tissue were (1) the composition of alpha-helixes increased in human cancerous colon tissue (15.30%) compared to normal colon tissue (11.72%); (2) beta-sheets which were 46.8% in healthy tissue decreased to 30.71% in cancer tissue; (3) beta-turns increased from 26.28% in normal tissue to 38.48% in cancer tissue; and (4) the composition of random coils was not significantly different between normal tissue (15.12%) and cancer tissue (15.51%). CONCLUSION: Our data demonstrate that protein in colon cancer displays abnormal FT-IR spectra. The conformational changes of the secondary structure of this protein in terms of alpha-helixes, beta-sheets and beta-turns were observed in normal and cancerous tissue from the same individual were compared.

Aged↗

PubMed1998

Binding of transducin and transducin-derived peptides to rhodopsin studies by attenuated total reflection-Fourier transform infrared difference spectroscopy.

Fourier transform infrared difference spectroscopy combined with the attenuated total reflection technique allows the monitoring of the association of transducin with bovine photoreceptor membranes in the dark. Illumination causes infrared absorption changes linked to formation of the light-activated rhodopsin-transducin complex. In addition to the spectral changes normally associated with meta II formation, prominent absorption increases occur at 1735 cm-1, 1640 cm-1, 1550 cm-1, and 1517 cm-1. The D2O sensitivity of the broad carbonyl stretching band around 1735 cm-1 indicates that a carboxylic acid group becomes protonated upon formation of the activated complex. Reconstitution of rhodopsin into phosphatidylcholine vesicles has little influence on the spectral properties of the rhodopsin-transducin complex, whereas pH affects the intensity of the carbonyl stretching band. AC-terminal peptide comprising amino acids 340-350 of the transducin alpha-subunit reproduces the frequencies and isotope sensitivities of several of the transducin-induced bands between 1500 and 1800 cm-1, whereas an N-terminal peptide (aa 8-23) does not. Therefore, the transducin-induced absorption changes can be ascribed mainly to an interaction between the transducin-alpha C-terminus and rhodopsin. The 1735 cm-1 vibration is also seen in the complex with C-terminal peptides devoid of free carboxylic acid groups, indicating that the corresponding carbonyl group is located on rhodopsin.

Amino Acid Sequence↗

PubMed1988

[In vivo analysis of the skin by Fourier-transformed infrared spectroscopy].

Advantages of Fourier transform infrared spectroscopy using reflexion techniques are used for skin analyses. Several examples of spectra obtained with a skin analyser are given and the major absorptions in the range 3,500 to 1,150 cm-1 are assigned to fundamental vibrations. Some of them can be used to determine the hydratation level of the skin.

Body Water↗

PubMed1999

Structure of a histidine ligand in the photosynthetic oxygen-evolving complex as studied by light-induced fourier transform infrared difference spectroscopy.

Fourier transform infrared (FTIR) signals of a histidine side chain were identified in flash-induced S(2)/S(1) difference spectra of the oxygen-evolving complex (OEC) of photosystem II (PS II) using PS II membranes from globally (15)N-labeled spinach and PS II core complexes from Synechocystis cells in which both the imidazole nitrogens of histidine were selectively labeled with (15)N. A negative band at 1113-1114 cm(-1) was downshifted by 7 cm(-1) upon both global (15)N-labeling and selective [(15)N]His labeling, and assigned to the C-N stretching mode of the imidazole ring. This band was unaffected by H-D exchange in the PS II preparations. In addition, several peaks observed at 2500-2850 cm(-1) all downshifted upon global and selective (15)N-labeling. These were ascribed to Fermi resonance peaks on a hydrogen-bonding N-H stretching band of the histidine side chain. FTIR measurements of model compounds of the histidine side chain showed that the C-N stretching band around 1100 cm(-)(1) can be a useful IR marker of the protonation form of the imidazole ring. The band appeared with frequencies in the following order: Npi-protonated (>1100 cm(-1)) > imidazolate > imidazolium > Ntau-protonated (<1095 cm(-1)). The frequency shift upon N-deuteration was occurred in the following order: imidazolium (15-20 cm(-1)) > Ntau-protonated (5-10 cm(-1)) > Npi-protonated approximately imidazolate ( approximately 0 cm(-1)). On the basis of these findings together with the Fermi resonance peaks at >2500 cm(-1) as a marker of N-H hydrogen-bonding, we concluded that the histidine residue in the S(2)/S(1) spectrum is protonated at the Npi site and that this Npi-H is hydrogen bonded. This histidine side chain probably ligated the redox-active Mn ion at the Ntau site, and thus, oxidation of the Mn cluster upon S(2) formation perturbed the histidine vibrations, causing this histidine to appear in the S(2)/S(1) difference spectrum.

Cyanobacteria↗

PubMed2000

A modified diffuse reflectance infrared Fourier transform spectroscopy cell for depth profiling of ceramic fibers.

A modified diffused reflectance infrared Fourier transformed spectroscopy (DRIFTS) accessory was used to analyze the surface properties of alumino-silicate fibers. The modifications are simple and involve a different way of performing depth-profiling from traditional DRIFTS by removing approximately 2 mm of salt from a full cup prior to placing the sample in for depth profiling. This method proved successful in elucidating the effects of quenching alumino-silicate fibers in mineral oil versus quenching in an air stream.

Aluminum Silicates↗

PubMed1999

Identification of dermatophytes by Fourier transform infrared spectroscopy (FT-IR).

Fourier transform infrared spectroscopy is an established method in the routine diagnosis of various micro-organisms, including bacteria and yeasts, on a species level. Its possible value in the diagnostics of dermatophytes was analysed using three clinical isolates each of the three most frequently found species, namely Trichophyton rubrum, Trichophyton mentagrophytes and Microsporum canis. The results encourage further work to establish a library which would allow the use of this method in the clinical setting. This might help to make repeated subcultures, which are money- and time-consuming, redundant.

Arthrodermataceae↗

PubMed2004

[Identification of edible mushrooms by Fourier transform infrared spectroscopy].

In this paper, Fourier transform infrared spectroscopy (FTIR) was used to identify edible mushrooms belonging to Auriculariales, Aphyllophorales, and Agaricales of Basidiomycotina. Vibrational spectra of fruiting bodies of ten species belonging to nine different genera of mushrooms (one is cultivated, and the others are wild growing) were recorded. The spectra were divided into five regions, i.e. 3 050 to 2 800 cm(-1), 1 750 to 1 500 cm(-1), 1 500 to 1 200 cm(-1), 1 200 to 950 cm(-1), and 950 to 700 cm(-1). These regions contain characteristic bands among different mushrooms. According to the characteristic bands in the five regions, different species of mushrooms can be identified. Vibrational spectra in the interval between 950 and 700 cm(-1) could serve as fingerprints to discriminate different genera of mushrooms.

Agaricales↗

PubMed2002

Analysis of C60 and C70 fullerenes using high-performance liquid chromatography-fourier transform infrared spectroscopy.

The performance of Fourier transform infrared spectroscopy (FT-IR) detection coupled to high-performance liquid chromatography for the analysis of C60 and C70 fullerenes was investigated. The isocratic separation method involved an octadecylsilane (ODS) column and an acetonitrile-toluene (1:1) mobile phase. The hyphenated system was designed with a split valve to control eluent volume leading to the FT-IR detector; this allowed for additional coupling of the liquid chromatograph to ultraviolet-visible detection. On-line FT-IR spectra of C60 and C70 were matched with standard off-line FT-IR spectra from the literature. In addition, with band chromatograms individual fullerenes can be identified using FT-IR active modes known specifically for each fullerene. Few changes to a pre-existing HPLC-UV method were necessary for the HPLC-FT-IR method, and there was no need for fraction collection to identify the fullerenes C60 and C70.

Chromatography, High Pressure Liquid↗

PubMed1996

Hydrogen/deuterium exchange kinetics of apolipophorin-III in lipid-free and phospholipid-bound states. An analysis by Fourier transform infrared spectroscopy.

Attenuated total reflection Fourier transform infrared spectroscopy was used to probe the kinetics of hydrogen/deuterium exchange in Manduca sexta apolipophorin-III (apoLp-III). ApoLp-III is an exchangeable apolipoprotein that is made up of five elongated amphipathic alpha-helices in a helical bundle conformation in the monomeric lipid-free form. Upon interaction with phospholipids, it is postulated to undergo a large conformational change whereby the hydrophobic interior is exposed, facilitating binding to the lipid surfaces. We have used the lipid-free and dimyristoylphosphatidylcholine-bound apoLp-III to study the dynamically variable domains in the two forms. Three populations of amide protons varying in their hydrogen/deuterium exchange rates were found to exist: slow, intermediate, and fast exchanging, which could correspond to completely buried, partially buried, and solvent-exposed domains on the protein in both the states. In lipid-free apoLp-III, 36, 12, and 52% of the total residues contributed to the slow, intermediate, and fast exchanging populations, respectively. In the dimyristoylphosphatidylcholine-bound form, the corresponding distribution was 20, 16, and 64%, representing a 12% increase in the number of exposed residues. The results are discussed in terms of increased solvent accessibility due to gross tertiary structural reorganization.

Amides↗

PubMed2000

The mechanism of GTP hydrolysis by Ras probed by Fourier transform infrared spectroscopy.

Time-resolved Fourier transform infrared spectroscopy (FTIR) in combination with photo-induced release of (18)O-labeled caged nucleotide has been employed to address mechanistic issues of GTP hydrolysis by Ras protein. Infrared spectroscopy of Ras complexes with nitrophenylethyl (NPE)-[alpha-(18)O(2)]GTP, NPE-[beta-(18)O(4)]GTP, or NPE-[gamma-(18)O(3)]GTP upon photolysis or during hydrolysis afforded a substantially improved mode assignment of phosphoryl group absorptions. Photolysis spectra of hydroxyphenylacyl-GTP and hydroxyphenylacyl-GDP bound to Ras and several mutants, Ras(Gly(12))-Mn(2+), Ras(Pro(12)), Ras(Ala(12)), and Ras(Val(12)), were obtained and yielded valuable information about structures of GTP or GDP bound to Ras mutants. IR spectra revealed stronger binding of GDP beta-PO(3)(2-) moiety by Ras mutants with higher activity, suggesting that the transition state is largely GDP-like. Analysis of the photolysis and hydrolysis FTIR spectra of the [beta-nonbridge-(18)O(2), alphabeta-bridge-(18)O]GTP isotopomer allowed us to probe for positional isotope exchange. Such a reaction might signal the existence of metaphosphate as a discrete intermediate, a key species for a dissociative mechanism. No positional isotope exchange was observed. Overall, our results support a concerted mechanism, but the transition state seems to have a considerable amount of dissociative character. This work demonstrates that time-resolved FTIR is highly suitable for monitoring positional isotope exchange and advantageous in many aspects over previously used methods, such as (31)P NMR and mass spectrometry.

Guanosine Triphosphate↗

PubMed1999

Relationships between conformation of beta-lactoglobulin in solution and gel states as revealed by attenuated total reflection Fourier transform infrared spectroscopy.

Attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR) has been used to compare the structure of beta-lactoglobulin, the major component of whey proteins, in solution and in its functional gel state. To induce variation in the conformation of beta-lactoglobulin under a set of gelling conditions, the effect of heating temperature, pH, and high pressure homogenization on the conformation sensitive amide I band in the infrared spectra of both solutions and gels has been investigated. The results showed that gelification process has a pronounced effect upon beta-lactoglobulin secondary structure, leading to the formation of intermolecular hydrogen-bonding beta-sheet structure as evidenced by the appearance of a strong band at 1614 cm(-1) at the expense of other regular structures. These results confirm that this structure may be essential for the formation of a gel network as it was previously shown for other globular proteins. However, this study reveals, for the first time, that there is a close relationship between conformation of beta-lactoglobulin in solution and its capacity to form a gel. Indeed, it is shown that conditions which promote predominance of intermolecular beta-sheet in solution such as pH 4, prevent the formation of gel in conditions used by increasing thermal stability of beta-lactoglobulin. On the basis of these findings, it is suggested that by controlling the extent of intermolecular beta-structure of the protein in solution, it is possible to modify the ability of protein to form a gel and as a consequence to control the properties of gels.

Gels↗

PubMed1995

Temperature-induced changes in protein structures studied by Fourier transform infrared spectroscopy and global analysis.

Fourier transform infrared (FTIR) spectroscopy has been used to study temperature-induced structural changes which occur in albumin, immunoglobulin G, fibrinogen, lysozyme, alpha-lactalbumin, and ribonuclease S when dissolved in 2H2O. In order to analyze the data, a new method was developed in which the data were analyzed globally with the aid of a spectral model. Seven or eight bands were sufficient to fit the full data set of spectra ranging from 1420 to 1760 cm-1 with a root mean square error of 1-2% of the maximum. Subsequently, the estimated band amplitude curves which showed a sigmoidal progression with increasing temperature were (globally) fitted with a two-state thermodynamic model. In this way, information on structural changes as well as on the thermal stability of the proteins was obtained. In all proteins investigated, enhanced 1H-2H exchange occurred at temperatures well below the unfolding of the secondary structure. This was interpreted as a change in tertiary structure leading to enhanced solvent accessibility. In all the proteins investigated, except for ribonuclease S, an intermolecular beta-sheet band indicative of aggregation appeared concomitant with the denaturation of the secondary structure. The results are compared with data from other techniques and discussed in terms of local unfolding and folding intermediates.

Animals↗

PubMed1996

Membrane fluidity response to odorants as seen by 2H-NMR and infrared spectroscopy.

Fourier transform infrared spectroscopy (FTIR) and deuterium nuclear magnetic resonance spectroscopy (2H-NMR) have been used to study the location of two odorants, beta-ionone and menthone, in a model membrane of dimyristoylphosphatidylcholine, as well as the effect of the odorants on the structure and dynamics of the phospholipids. The interaction has been investigated for two lipid-to-odorant molar ratios, 10:1 and 1:1. The two odorants were found to affect the fluidity of the membrane. More specifically, the 2H-NMR results indicate that at a lipid-to-odorant molar ratio of 10:1, both beta-ionone and menthone increase the order of the deuterons in the interfacial and headgroup regions of the lipid while the incorporation of the odorants at a lipid-to-odorant molar ratio of 1:1 decreases the order of both the lipid headgroup and acyl chains. On the other hand, the infrared results show that the incorporation of beta-ionone and menthone decreases the phase transition temperature and cooperativity of the lipid acyl chains. The results suggest that the site of incorporation of beta-ionone and menthone is very similar in DMPC membranes.

Dimyristoylphosphatidylcholine↗