Nanosecond time-resolved absorption studies of human oxyhemoglobin photolysis intermediates

Simultaneous photoreduction and Raman spectroscopy of red blood cells to investigate the effects of organophosphate exposure

Simultaneous photoreduction and Raman spectroscopy with 532 nm laser has been used to study the effects of organophosphate (chlorpyrifos [CPF]) exposure on human red blood cells (RBCs). Since in RBCs, auto-oxidation causes oxidative stress, which, in turn, is balanced by the cellular detoxicants, any possible negative effect of CPF on this balance should results in an increased level of damaged (permanently oxygenated) hemoglobin. Therefore, when 532 nm laser, at a suitable power, was applied to photoreduce the cells, only common oxygenated form of hemoglobin got photoreduced leaving the permanently oxygenated hemoglobin detectable in the Raman spectra simultaneously excited by the same laser. Using the technique effects of CPF to build up oxidative stress on RBCs could be detected at concentrations as low as 10 ppb from a comparison of relative strengths of different Raman bands. Experiments performed using simultaneously exposing the cells, along with CPF, to H₂ O₂ (oxidative agent) and/or 3-Aminotriazole (inhibitor of anti-oxidant catalase), suggested role of CPF to suppress the cellular anti-oxidant mechanism. Since the high level of damaged hemoglobin produced by the action of CPF (at concentrations >100 ppm) is expected to cause membrane damage, atomic force microscopy (AFM) was used to identify such damages.Upper panel: Raman spectra of normal, photoreduced CPF exposed and unexposed RBCs. Lower panel: The weak Fe-O₂ Raman band for CPF exposed cells shown on the left. The AFM images of unexposed and exposed cells are shown on the right. Scale bar, 2.5 μm.

Local changes in arterial oxygen saturation induced by visible and near-infrared light radiation

In this study, we investigate the efficiency of laser radiation on oxyhemoglobin (HbO2) rate in blood vessels and its wavelength dependence. The results of in vivo experimental measurements of the laser-induced photodissociation of HbO2 in cutaneous blood vessels in the visible and near-infrared (IR) spectral range are presented. Arterial oxygen saturation (SpO2) was measured by a method of fingertip pulse oximetry, which is based on the measurement of the modulated pulse wave of the blood. The light irradiating the finger was provided by corresponding light-emitting diodes (LED) at 15 wavelengths in the 400-940 nm spectrum range. Statistical results with a value of p < 0.05 were viewed as being significant for all volunteers. The results show that there is a decrease in SpO2 in the blood under the influence of the transcutaneous laser irradiation. Three maxima in the spectral range (530, 600, and 850 nm) are revealed, wherein decrease in the relative concentration of SpO2 reaches 5 % ± 0.5 %. Near-IR radiation plays a dominant role in absorption of laser radiation by oxyhemoglobin in deeper layers of tissue blood vessels. The obtained data correlate with the processes of light propagation in biological tissue. The observed reduction in SpO2 indicates the process of photodissociation of HbO2 in vivo and may result in local increase in O2 in the tissue. Such laser-induced enrichment of tissue oxygenation can be used in phototherapy of pathologies, where the elimination of local tissue hypoxia is critical.

Photolyses of mammalian oxy-hemoglobin studied by nanosecond photoacoustic calorimetry

Enthalpy and conformational volume changes in photolyses of oxy-hemoglobin (HbO(2)) of human, bovine, pig, horse and rabbit are investigated by photoacoustic calorimetry. In the experiment, a pulsed Nd:YAG laser is used as an exciting source, and a PVDF film transducer and a PZT transducer are used to detect the photoacoustic signals. Based on the time scales of the excitation and detection systems as well as the photolysis processes of HbO(2), it can be indicated that the measured enthalpy and conformational volume changes are related to slow geminate recombination and tertiary relaxation in photolyses of HbO(2), which are with the time scale of 30-40 ns and 100-150 ns, respectively. The results show that the enthalpy and conformational volume changes are different for both photolysis processes of HbO(2) and also for various mammals. The different results among the five mammals are analyzed and discussed briefly.

Photo-dissociation quantum yields of mammalian oxyhemoglobin investigated by a nanosecond laser technique

The photo-dissociations of oxyhemoglobin of several mammals, such as human, bovine, pig, horse, and rabbit, have been studied. By means of optical pump-probe technique, the quantum yields for photo-dissociation of these oxyhemoglobin have been determined at pH 7 and 20 degrees C. A nanosecond laser at 532 nm is used as the pumping source, and a xenon lamp through a monochrometer provides a probe light at 432 nm. The experimental results show that the quantum yields of these mammalian oxyhemoglobin are different from each other, especially for that of rabbit. By analyzing the amino acid sequences and tetramer structures as well as the flexibility and hydrophobicity of the different hemoglobin, possible explanations for the differences are proposed.

Enthalpy and conformational volume changes of mammalian oxy-hemoglobins investigated by pulsed photoacoustic calorimetry

Enthalpy and conformational volume changes induced by laser photo-dissociation reactions of mammalian oxy-hemoglobin, such as human, bovine, pig, horse and rabbit oxy-hemoglobins, are investigated by pulsed photoacoustic calorimetry. Generally, the response time of the photoacoustic calorimetry is restricted by the width of the laser pulse and the bandwidth of the acoustic detector. Considering the time window of the experimental system, the enthalpy and conformational volume changes detected should be caused by the tertiary relaxation of the heme proteins. In order to calculate the enthalpy and conformational volume changes, the quantum yields of the photo-dissociation products of oxy-hemoglobins must be measured and taken into account. Finally, the enthalpy and conformational volume changes of the oxy-hemoglobins connected with the tertiary relaxation are obtained, which show that for all measured mammalian oxy-hemoglobins the values of enthalpy changes are in the range of 30.0-46.8 kcal/mol and volume changes are of 2.3-7.8 ml/mol although the quantum yields for the different species may have much bigger differences. A possible explanation of the results is presented.

Spectroscopic and Functional Characterization of T State Hemoglobin Conformations Encapsulated in Silica Gels

Oxygen binding curves of sol-gel-encapsulated deoxy human adult hemoglobin (HbA) have previously revealed two distinct noncooperative populations with oxygen binding affinities approximately 1000 and 100 times lower than that of the high-affinity R state. The two populations which have been termed the low-affinity (LA) and high-affinity (HA) T states can be selectively stabilized using two different encapsulation protocols for deoxy-HbA. The present study seeks to understand the factors giving rise to these different affinity states. Visible and UV resonance Raman spectroscopies are used to characterize the conformational properties of both the deoxy and deoxy-turned-carbonmonoxy (CO) derivatives of HbA derived from the two encapsulation protocols. The geminate and bimolecular recombination of CO to the photodissociated CO derivatives is used to characterize the functional properties of the slowly evolving encapsulated populations. The results show that the initial deoxy-HbA populations are conformationally indistinguishable with respect to encapsulation protocol. The addition of CO to sol-gel-encapsulated deoxy-HbA triggers a detectable progression of conformational and functional changes. Visible resonance Raman spectra of the CO photoproduct reveal a progression of changes of the iron-proximal histidine stretching frequencies: 215, 222, 227, and 230 cm(-1). The low and high values correspond to the initial deoxy T state and liganded R (R(2)) state species, respectively. The 222 and 227 cm(-1) species are generated using encapsulation protocols that give rise to what are termed the LA and HA T states, respectively. The UV resonance Raman spectra of these and related species indicate that the progression from deoxy T to LA to HA is associated with a progressive loosening of T state constraints within the hinge and switch regions of the alpha(1)beta(2) interface. The time scale for the progression is determined by a balance between the ligation-initiated evolution toward high-affinity conformations and factors such as allosteric effectors, gel matrix, and added glycerol that slow ligand-binding-induced relaxation. Thus, it appears that the encapsulation protocol-dependent rate of ligand-binding-induced relaxation determines the functional properties of the initially encapsulated deoxy-HbA population.

Laser-induced time-resolved photoacoustic calorimetry study on photo-dissociation of human and bovine oxyhemoglobin

The dynamics of the enthalpy and volume changes related to the photo-dissociation of oxygen from human and bovine oxyhemoglobin are investigated by nanosecond time-resolved photoacoustic calorimetry (PAC). The values of enthalpy and volume change associated with the above process are deltaH = 37.8 +/- 3 kcal/mol, deltaV = 5.0 +/- 1 ml/mol for human HbO(2); and deltaH = 35.7 +/- 3.5 kcal/mol, deltaV = 4.8 +/- 1 ml/mol for bovine HbO(2), respectively. A possible explanation for the similar values between both human and bovine oxyhemoglobin is proposed. In addition, the PAC results for human HbO(2) and HbCO are compared and discussed.

Rapid spectrophotometric determination of oxygen consumption using hemoglobin, in vitro: light scatter correction and expanded dynamic range

The method of using absorbance in conjunction with hemoglobin (Hb) to monitor rapid changes in oxygen consumption in vitro was improved by using a non-linear calibration technique and multiwavelength spectroscopy. The O(2) dependence of Hb absorbance was effectively linearized using the current technique (R(2) = 0.990+/-0.002, n = 3), and extended the dynamic range of [O(2)] determinations by 1.6-fold over previous approaches. The association/dissociation rates of O(2) and Hb were evaluated using the current approach and were not significant on the 100-ms time domain. A method was also developed for compensating for large amplitude light scattering changes in turbid media using multiwavelength analysis. Both the nonlinear calibration curve and light scattering corrections were validated in isolated porcine heart mitochondrial preparations.

Low temperature photolysis of denatured nitrosyl hemoproteins

Photolysis of denatured HbNO were carried out at temperatures below 26 K. The normalized kinetic curves were fitted using either two exponentials or a conformational substate energy distribution or a fractal model. The parameters are related to the protein structure. The two exponentials model assumes the existence of two fractions of photolysed molecules that rebind with slow and fast reaction rates. Only the slow reaction rate is sensitive to the denaturation process. The pre-exponential factor and the peak energy of the substate distribution values suggest an increase in the entropy and a decrease of the flexibility in the denatured samples, respectively. The fractal model parameters strengthened the functional relevance of the flexibility of the protein chain.

Evidence for heme-heme excitonic coupling in the Soret circular dichroism of hemoglobin

In order to study interdimer heme-heme electronic interactions in human hemoglobin, the Soret circular dichroism spectrum of the carboxy adduct is measured as a function of protein concentration, the spectrum at the highest concentration representing primarily that of alpha2beta2 tetramers (93%) and the lowest concentration representing primarily alphabeta dimers (68%). The tetramer-dimer difference spectrum, obtained using singular value decomposition and linear least squares fitting from a matrix of CD spectra measured at ten concentrations, is roughly conservative, with a larger negative lobe at shorter wavelengths and a peak-to-trough magnitude that is 18% of the tetramer's maximum Soret CD magnitude. It is tentatively assigned to heme-heme excitonic interactions on the basis of theoretical predictions by R. W. Woody [(1985) in Optical Properties and Structure of Tetrapyrroles (Blauer, G., and Sund, H., Eds.), pp. 239-256, Walter de Gruyter, New York].

Nanosecond time-resolved spectroscopy of biomolecular processes

Over the past two decades, nanosecond absorption and vibrational spectroscopies have developed into powerful tools for monitoring the secondary, tertiary, and quaternary structural relaxations of biological macromolecules under near-physiological conditions of solvent and temperature. Observed through such methods, the dynamic response of a biomolecule to photoinitiated excursions from equilibrium can reveal valuable information about the structure-function relationship, information beyond that obtained from the static structures provided by X-ray crystallography, nuclear magnetic resonance spectroscopy, and other steady-state methods. Most recently, the development of ultra-sensitive polarization techniques for absorption spectroscopy has greatly enhanced the amount of time-resolved structural information that can be obtained from the broadened electronic spectra of biomolecules. This review examines nanosecond absorption, vibrational, and polarized absorption methods, and their applications to protein function and folding, emphasizing the complementary nature of information obtained from electronic and vibrational spectra measured on the nanosecond time scale.