Resonance Raman microspectroscopic characterization of eosinophil peroxidase in human eosinophilic granulocytes

Multi-wavelength Raman microscopy of nickel-based electron transport in cable bacteria

Cable bacteria embed a network of conductive protein fibers in their cell envelope that efficiently guides electron transport over distances spanning up to several centimeters. This form of long-distance electron transport is unique in biology and is mediated by a metalloprotein with a sulfur-coordinated nickel (Ni) cofactor. However, the molecular structure of this cofactor remains presently unknown. Here, we applied multi-wavelength Raman microscopy to identify cell compounds linked to the unique cable bacterium physiology, combined with stable isotope labeling, and orientation-dependent and ultralow-frequency Raman microscopy to gain insight into the structure and organization of this novel Ni-cofactor. Raman spectra of native cable bacterium filaments reveal vibrational modes originating from cytochromes, polyphosphate granules, proteins, as well as the Ni-cofactor. After selective extraction of the conductive fiber network from the cell envelope, the Raman spectrum becomes simpler, and primarily retains vibrational modes associated with the Ni-cofactor. These Ni-cofactor modes exhibit intense Raman scattering as well as a strong orientation-dependent response. The signal intensity is particularly elevated when the polarization of incident laser light is parallel to the direction of the conductive fibers. This orientation dependence allows to selectively identify the modes that are associated with the Ni-cofactor. We identified 13 such modes, some of which display strong Raman signals across the entire range of applied wavelengths (405-1,064 nm). Assignment of vibrational modes, supported by stable isotope labeling, suggest that the structure of the Ni-cofactor shares a resemblance with that of nickel bis(1,2-dithiolene) complexes. Overall, our results indicate that cable bacteria have evolved a unique cofactor structure that does not resemble any of the known Ni-cofactors in biology.

Combining fiber optical tweezers and Raman spectroscopy for rapid identification of melanoma

Cutaneous melanoma is a skin tumor with a high degree of malignancy and fatality rate, the incidence of which has increased in recent years. Therefore, a rapid and sensitive diagnostic technique of melanoma cells is urgently needed. In this paper, we present a new approach using fiber optical tweezers to manipulate melanoma cells to measure their Raman spectra. Then, combined with Principal Component Analysis and Support Vector Machines (PCA-SVM) classification model, to achieve the classification of common mutant, wild-type and drug-resistant melanoma cells. A total of 150 Raman spectra of 30 cells were collected from mutant, wild-type and drug-resistant melanoma cell lines, and the classification accuracy was 92%, 94%, 97.5%, respectively. These results suggest that the study of tumor cells based on fiber optical tweezers and Raman spectroscopy is a promising method for early and rapid identification and diagnosis of tumor cells.

Eosinophils and Neutrophils-Molecular Differences Revealed by Spontaneous Raman, CARS and Fluorescence Microscopy

Leukocytes are a part of the immune system that plays an important role in the host’s defense against viral, bacterial, and fungal infections. Among the human leukocytes, two granulocytes, neutrophils (Ne) and eosinophils (EOS) play an important role in the innate immune system. For that purpose, eosinophils and neutrophils contain specific granules containing protoporphyrin-type proteins such as eosinophil peroxidase (EPO) and myeloperoxidase (MPO), respectively, which contribute directly to their anti-infection activity. Since both proteins are structurally and functionally different, they could potentially be a marker of both cells’ types. To prove this hypothesis, UV−Vis absorption spectroscopy and Raman imaging were applied to analyze EPO and MPO and their content in leukocytes isolated from the whole blood. Moreover, leukocytes can contain lipidic structures, called lipid bodies (LBs), which are linked to the regulation of immune responses and are considered to be a marker of cell inflammation. In this work, we showed how to determine the number of LBs in two types of granulocytes, EOS and Ne, using fluorescence and coherent anti-Stokes Raman scattering (CARS) microscopy. Spectroscopic differences of EPO and MPO can be used to identify these cells in blood samples, while the detection of LBs can indicate the cell inflammation process.

Raman imaging highlights biochemical heterogeneity of human eosinophils versus human eosinophilic leukaemia cell line

Eosinophils are acidophilic granulocytes that develop in the bone marrow. Although their population contributes only to approximately 1-6% of all leucocytes present in the human blood, they possess a wide range of specific functions. They play a key role in inflammation-regulating processes, when their numbers can increased to above 5 × 10⁹ /l of peripheral blood. Their characteristic feature is the presence of granules containing eosinophil peroxidase (EPO), the release of which can trigger a cascade of events promoting oxidative stress, apoptosis or necrosis, leading finally to cell death. Raman spectroscopy is a powerful technique to detect EPO, which comprises a chromophore protoporphyrin IX. Another cell structure associated with inflammation processes are lipid bodies (lipid-rich organelles), also well recognized and imaged using high resolution confocal Raman spectroscopy. In this work, eosinophils isolated from the blood of a human donor were analysed versus their model, EoL-1 human eosinophilic leukaemia cell line, by Raman spectroscopic imaging. We showed that EPO was present only in primary cells and not found in the cell line. Eosinophils were activated using phorbol 12-myristate 13-acetate, which resulted in lipid bodies formation. An effect of cells stimulation was studied and compared for eosinophils and EoL-1.

Changes in hemoglobin-oxygen affinity with shape variations of red blood cells

Shape variations of red blood cells (RBCs) are known to occur upon exposure to various drugs or under diseased conditions. The commonly observed discocytic RBCs can be transformed to echinocytic or stomatocytic shape under such conditions. Raman spectra of the three major shape variations, namely discocyte, echinocyte, and stomatocyte, of RBCs were studied while subjecting the cells to oxygenated and deoxygenated conditions. Analysis of the recorded spectra suggests an increased level of hemoglobin (Hb)-oxygen affinity for the echinocytes. Also, some level of Hb degradation could be noticed for the deoxygenated echinocytes. The effects may arise from a reduced level of intracellular adenosine triphosphate in echinocytic cells and an increased fraction of submembrane Hb.

Effects of acute hypoxic exposure on oxygen affinity of human red blood cells

Adaptation of red blood cells subjected to acute hypoxia, crucial for managing high altitude syndrome and pulmonary diseases, has been investigated. For this, red blood cells were exposed to the acute hypoxic condition by purging nitrogen over increasing time periods from 15 to 60 min and thereafter equilibrated with atmospheric oxygen for 10 min. Raman spectra of these red blood cells were then recorded and analyzed to look for changes in the level of oxygenation compared to unexposed cells. A decreasing oxygen affinity for the cells was observed with increasing time of exposure to the hypoxic condition. This change in oxygen affinity for the red blood cells may result from metabolic adjustment of the cells under the hypoxic condition to promote increased concentration of intracellular 2, 3-diphosphoglycerate.

Deciphering the Finger Prints of Brain Cancer Glioblastoma Multiforme from Four Different Patients by Using Near Infrared Raman Spectroscopy

To explore the effectiveness of Raman spectra to diagnose brain cancer glioblastoma multiforme (GBM), we investigated the Raman spectra of single cell from four different GBM cell lines developed from four different patients and analyzed the spectra. The Raman spectra of brain cancer (GBM) cells were similar in all these cell lines. The results indicate that Raman spectra can offer the experimental basis for the cancer diagnosis and treatment.

Resonance Raman spectroscopy in malaria research

In recent years, the field of Raman spectroscopy has witnessed a surge in technological development, with the incorporation of ultrasensitive, charge-coupled devices, improved laser sources and precision Rayleigh-filter systems. This has led to the development of sensitive confocal micro-Raman spectrometers and imaging spectrometers that are capable of obtaining high spatial-resolution spectra and images of subcellular components within single living cells. This review reports on the application of resonance micro-Raman spectroscopy to the study of malaria pigment (hemozoin), a by-product of hemoglobin catabolization by the malaria parasite, which is an important target site for antimalarial drugs. The review aims to briefly describe recent studies on the application of this technology, elucidate molecular and electronic properties of the malaria pigment and its synthetic analog beta-hematin, provide insight into the mechanism of hemozoin formation within the food vacuole of the parasite, and comment on developing strategies for using this technology in drug-screening protocols.

Raman microspectroscopy: a noninvasive tool for studies of individual living cellsin vitro

There is an increasing need for noninvasive methods that are able to monitor individual live cells in vitro, including in vitro testing of chemicals and pharmaceuticals, monitoring the growth of engineered tissues and the development of cell-based biosensors. Raman spectroscopy is a pure optical technique based on inelastic scattering of laser photons by molecular vibrations of biopolymers, which provide a chemical fingerprint of cells or organelles without fixation, lysis or the use of labels and other contrast-enhancing chemicals. Changes in cells during the cell cycle, cell death, differentiation or during the interaction with various chemicals or materials involve biochemical changes that can be measured with high spatial ( approximately 300 nm) and temporal (seconds to minutes) resolution. The latest technological developments, especially high-sensitivity charged coupled detectors and high-power near-infrared lasers, have spurred the growth of Raman microspectroscopy towards being a well established analytical tool. This review covers the recent applications of this technique, including studies of individual cells, both pro- and eukaryotes, and emphasizes the potential impact on modern scientific endeavors, such as tissue engineering and drug discovery.

Preservation of 5300 year old red blood cells in the Iceman

Changes in elasticity and structures of red blood cells (RBCs) are important indicators of disease, and this makes them interesting for medical studies. In forensics, blood analyses represent a crucial part of crime scene investigations. For these reasons, the recovery and analysis of blood cells from ancient tissues is of major interest. In this study, we show that RBCs were preserved in Iceman tissue samples for more than 5000 years. The morphological and molecular composition of the blood corpuscle is verified by atomic force microscope and Raman spectroscopy measurements. The cell size and shape approximated those of healthy, dried, recent RBCs. Raman spectra of the ancient corpuscle revealed bands that are characteristic of haemoglobin. Additional vibrational modes typical for other proteinaceous fragments, possibly fibrin, suggested the formation of a blood clot. The band intensities, however, were approximately an order of magnitude weaker than those of recent RBCs. This fact points to a decrease in the RBC-specific metalloprotein haemoglobin and, thus, to a degradation of the cells. Together, the results show the preservation of RBCs in the 5000 year old mummy tissue and give the first insights into their degradation.

Studies on erythrocytes in malaria infected blood sample with Raman optical tweezers

Raman spectroscopy was performed on optically trapped red blood cells (RBCs) from blood samples of healthy volunteers (h-RBCs) and from patients suffering from P. vivax infection (m-RBCs). A significant fraction of m-RBCs produced Raman spectra with altered characteristics relative to h-RBCs. The observed spectral changes suggest a reduced oxygen-affinity or right shifting of the oxygen-dissociation curve for the intracellular hemoglobin in a significant fraction of m-RBCs with respect to its normal functional state.

Perturbed heme binding is responsible for the blistering phenotype associated with mutations in the Caenorhabditis elegans dual oxidase 1 (DUOX1) peroxidase domain

Dual oxidase (DUOX) enzymes support a wide variety of essential reactions, from cellular signaling to thyroid hormone biosynthesis. In Caenorhabditis elegans, the DUOX system (CeDUOX1/2) plays a crucial role in innate immunity and in stabilizing the cuticle by forming tyrosine cross-links. The current model suggests that superoxide generated by CeDUOX1 at the C-terminal NADPH oxidase domain is rapidly converted to H(2)O(2). The H(2)O(2) is then utilized by the N-terminal peroxidase-like domain to cross-link tyrosines. We have now created a series of mutations in the isolated peroxidase domain, CeDUOX1(1-589). One set of mutations investigate the roles of a putative distal tyrosine (Tyr(105)) and Glu(238), a proposed covalent heme-binding residue. The results confirm that Glu(238) covalently binds to the heme group. A second set of mutations (G246D and D392N) responsible for a C. elegans blistering cuticle phenotype was also investigated. Surprisingly, although not among the catalytic residues, both mutations affected heme co-factor binding. The G246D mutant bound less total heme than the wild type, but a higher fraction of it was covalently bound. In contrast, the D392N mutant appears to fold normally but does not bind heme. Molecular dynamics simulations of a CeDUOX1(1-589) homology model implicate displacements of the proximal histidine residue as the likely cause. Both enzymes are structurally stable and through altered heme interactions exhibit partial or complete loss of tyrosine cross-linking activity, explaining the blistering phenotype. This result argues that the CeDUOX peroxidase domain is primarily responsible for tyrosine cross-linking.

Deciphering the finger Prints of Brain Cancer Astrocytoma in comparison to Astrocytes by using near infrared Raman Spectroscopy

To explore the biochemical differences between brain cancer cells Astrocytoma and normal cells Astrocyte, we investigated the Raman spectra of single cell from these two cell types and analyzed the difference in spectra and intensity. Raman spectrum shows the banding pattern of different compounds as detected by the laser. Raman intensity measures the intensity of these individual bands. The Raman spectra of brain cancer cells was similar to those of normal cells, but the Raman intensity of cancer cells was much higher than that of normal cells. The Raman spectra of brain cancer Astrocytoma shows that the structural changes of cancer cells happen so that many biological functions of these cells are lost. The results indicate that Raman spectra can offer the experimental basis for the cancer diagnosis and treatment.

Combined Fourier transform infrared and Raman spectroscopic approach for identification of multidrug resistance phenotype in cancer cell lines

Cancer cells escape cytotoxic effects of anticancer drugs by a process known as multidrug resistance (MDR). Identification of cell status by less time-consuming methods can be extremely useful in patient management and treatment. This study aims at evaluating the potentials of vibrational spectroscopic methods to perform cell typing and to differentiate between sensitive and resistant human cancer cell lines, in particular those that exhibit the MDR phenotype. Micro-Raman and Fourier transform infrared (FTIR) spectra have been acquired from the sensitive promyelocytic HL60 leukemia cell line and two of its subclones resistant to doxorubicin (HL60/DOX) and daunorubicin (HL60/DNR), and from the sensitive MCF7 breast cancer cell line and its MDR counterpart resistant to verapamil (MCF7/VP). Principal components analysis (PCA) was employed for spectral comparison and classification. Our data show that cell typing was feasible with both methods, giving two distinct clusters for HL60- and MCF7-sensitive cells. In addition, phenotyping of HL60 cells, i.e., discriminating between the sensitive and MDR phenotypes, was attempted by both methods. FTIR could not only delineate between the sensitive and resistant HL60 cells, but also gave two distinct clusters for the resistant cells, which required a two-step procedure with Raman spectra. In the case of MCF7 cell lines, both the sensitive and resistant phenotypes could be differentiated very efficiently by PCA analysis of their FTIR and Raman point spectra. These results indicate the prospective applicability of FTIR and micro-Raman approaches in the differentiation of cell types as well as characterization of the cell status, such as the MDR phenotype exhibited in resistant leukemia cell lines like HL60 and MCF7.

Activation-dependent phases of T cells distinguished by use of optical tweezers and near infrared Raman spectroscopy

Near-infrared Raman spectroscopy may provide a highly sensitive, noninvasive means to identify activation status of leukocytes. The purpose of the current study was to establish Raman spectroscopic characteristics of T cell activation. Activation of the RsL.11 T cell clone in vitro with Con A resulted in specific decrements in band intensities at 785, 1048, 1093, and 1376 cm(-1) but did not alter a majority of other band intensities including those at 1004 cm(-1) (phenylalanine) and 1660 cm(-1) (amide bonds). Activation-dependent decrements in these band intensities occurred subsequent to IL-2 production and correlated closely with T cell blastogenesis. Activation-dependent decrements in these band intensities were not strictly a function of cell size because the same observations were noted in size-controlled comparisons of resting and activated T cells. Like the RsL.11 clone, freshly isolated thymocytes that were activated by Con A or IL-2 showed decrements in particular emissions. These findings indicate that near-infrared Raman spectroscopy can be used as a noninvasive technique to reveal the activation status of single living T cells.

Raman microspectroscopy and imaging provides insights into heme aggregation and denaturation within human erythrocytes

The oxygenation process of a human erythrocyte is monitored using a Raman microimaging technique. Raman images of the 1638 cm(-1) band are recorded in the oxygenated and deoxygenated state using only 120 s of laser exposure and approximately 1 mW of defocused laser power. The images show hemoglobin oxygenating and deoxygenating within the cell. Prolonged laser imaging exposure (<180 s) at low temperatures results in photoinduced and/or thermal degradation. The effect of thermal degradation is investigated by recording spectra of erythrocytes as a function of temperature between 4 and 52 degrees C. Five bands at 1396, 1365, 1248, 972, and 662 cm(-1) are identified as markers for heme aggregation. Raman images recorded of cells after prolonged laser exposure appear to show heme aggregation commencing in the middle and moving toward the periphery of the cell. UV-visible spectra of erythrocytes show the Soret band to be broader and red shifted (approximately 3 nm) at temperatures between 45 and 55 degrees indicative of excitonic interactions. It is postulated that the enhancement of the aggregation marker bands observed at 632.8-nm excitation results primarily from excitonic interactions between the aggregated hemes in response to protein denaturation. The results have important medical implications in detecting and monitoring heme aggregation associated with hemopathies such as sickle cell disease.

Nonresonant confocal Raman imaging of DNA and protein distribution in apoptotic cells

Nonresonant confocal Raman imaging has been used to map the DNA and the protein distributions in individual single human cells. The images are obtained on an improved homebuilt confocal Raman microscope. After statistical analysis, using singular value decomposition, the Raman images are reconstructed from the spectra covering the fingerprint region. The data are obtained at a step interval of approximately 250 nm and cover a field from 8- to 15- micro m square in size. Dwell times at each pixel are between 0.5 and 2 s, depending on the nature and the state of the cell under investigation. High quality nonresonant Raman images can only be obtained under these conditions using continuous wave high laser powers between 60 and 120 mW. We will present evidence that these laser powers can still safely be used to recover the chemical distributions in fixed cells. The developed Raman imaging method is used to image directly, i.e., without prior labeling, the nucleotide condensation and the protein distribution in the so-called nuclear fragments of apoptotic HeLa cells. In the control (nonapoptotic) HeLa cells, we show, for the first time by Raman microspectroscopy, the presence of the RNA in a cell nucleus.

Micro-Raman characterization of high- and low-spin heme moieties within single living erythrocytes

Raman microspectroscopy was applied to monitor porphyrin perturbation associated with the tense-relaxed (T --> R) state transition of hemoglobin (Hb) within a single red blood cell. The spectra exhibited dramatic changes in the spin state region (1650-1500 cm(-1)) and the methine C-H deformation region (1250-1200 cm(-1)) between the 27- and 54-min interval following reoxygenation. Principal components analysis revealed a sigmoidal curve when the PC1 scores versus time were plotted. The inflection point on the curve corresponded to the T --> R transition point spectrum, indicating the cell is composed of Hb in a mixture of spin states. The results of this work illustrate the dynamics of porphyrin perturbation during erythrocyte respiration and may have applications in the diagnosis and treatment of red blood cell disorders including thalassemia and sickle cell anemia.

Sensitive disk resonator photonic biosensor

We describe a photonic device based on a high-finesse, whispering-gallery-mode disk resonator that can be used for the detection of biological pathogens. This device operates by means of monitoring the change in transfer characteristics of the disk resonator when biological materials fall onto its active area. High sensitivity is achieved because the light wave interacts many times with each pathogen as a consequence of the resonant recirculation of light within the disk structure. Specificity of the detected substance can be achieved when a layer of antibodies or other binding material is deposited onto the active area of the resonator. Formulas are presented that allow the sensitivity of the device to be quantified and that show that, under optimum conditions, as few as 100 molecules can be detected.

Micro-Raman characterisation of the R to T state transition of haemoglobin within a single living erythrocyte

We present the first recorded Raman spectra of haemoglobin in both the R and T states from within a single living erythrocyte using 632.8 nm excitation. Bands characteristic of low spin haems are observed in oxygenated and carboxylated erythrocytes at approx. 1636 (nu(10)), 1562-1565 (nu(2)), 1250-1245 cm(-1) (nu(13)) and 1226-1224 cm(-1) (nu(5)+nu(8)). The spectra of deoxygenated and methaemoglobin erythrocytes have characteristic high spin bands at approx. 1610-1606 cm(-1) (nu(10)), 1582-1580 (nu(37)), 1547-1544 (nu(11)), 1230-1220 cm(-1) (nu(13)) and 1215-1210 cm(-1) (nu(5)+nu(8)). Bands at 1172 (nu(30)), 976 (nu(45)) and 672 (nu(7)) cm(-1) appear to be enhanced at 632.8 nm in low spin haems. The oxidation state marker band (nu(4)) at 1364-1366 cm(-1) appeared invariant within this domain in all single cells and conditions investigated contrary to other resonance Raman studies on haem isolates. The information gained by in vivo single erythrocyte molecular analysis has important ramifications to the understanding of fundamental physiological processes and may have applications in the diagnosis and treatment of red blood cell disorders.

Eosinophil peroxidase oxidation of thiocyanate. Characterization of major reaction products and a potential sulfhydryl-targeted cytotoxicity system

Although the pseudohalide thiocyanate (SCN(-)) is the preferred substrate for eosinophil peroxidase (EPO) in fluids of physiologic halide composition, the product(s) of this reaction have not been directly identified, and mechanisms underlying their cytotoxic potential are poorly characterized. We used nuclear magnetic resonance spectroscopy (NMR), electrospray ionization mass spectrometry, and quantitative chemical analysis to identify the principal reaction products of both the EPO/SCN(-)/H(2)O(2) system and activated eosinophils as roughly equimolar amounts of OSCN(-) (hypothiocyanite) and OCN(-) (cyanate). Red blood cells exposed to increasing concentrations of OSCN(-)/OCN(-) are first depleted of glutathione, after which glutathione S-transferase and glyceraldehyde-3-phosphate dehydrogenase then ATPases undergo sulfhydryl (SH) reductant-reversible inactivation before lysing. OSCN(-)/OCN(-) inactivates red blood cell membrane ATPases 10-1000 times more potently than do HOCl, HOBr, and H(2)O(2). Exposure of glutathione S-transferase to [(14)C]OSCN(-)/OCN(-) causes SH reductant-reversible disulfide bonding and covalent isotope labeling. We propose that EPO/SCN(-)/H(2)O(2) reaction products comprise a potential SH-targeted cytotoxic system that functions in striking contrast to HOCl, the highly but relatively indiscriminantly reactive product of the neutrophil myeloperoxidase system.

Intracellular reactions in single human granulocytes upon phorbol myristate acetate activation using confocal Raman microspectroscopy

We have obtained new evidence for the occurrence of intracellular NADPH-oxidase activity in neutrophilic and eosinophilic granulocytes upon stimulation with phorbol myristate acetate (PMA). PMA activation leads to a partial translocation of cytochrome b(558) from the membranes of the specific granules to the plasma membrane. It was suggested that NADPH-oxidase activity only takes place in the plasma membrane, leading to an extracellular release of oxygen metabolites because cellular self-destruction can be avoided in this way. The effects of PMA activation were indirectly studied in recent experiments employing scavengers of extracellular superoxide anion and hydrogen peroxide, and support for intracellular NADPH-oxidase activity was obtained. In this paper we use Raman microspectroscopy as a direct method to study intracellular molecular reactions that result from cellular triggering by PMA. The molecular specificity of this microscopic method enables us to show that intracellular reduction of both myeloperoxidase (MPO) and cytochrome b(558) occurs in neutrophilic granulocytes. Control measurements with cytochrome b(558)-deficient neutrophilic granulocytes did not show a reduction of intracellular MPO. This is direct support for the occurrence of intracellular NADPH-oxidase activity in organelles that must be in close contact with the azurophilic granules that contain MPO. Furthermore, a comparison was made with chemical reactions occurring in eosinophilic granulocytes after activation with PMA. Moreover, in these cells an intracellular reduction of eosinophil peroxidase was observed.

Biochemical evidence for heme linkage through esters with Asp-93 and Glu-241 in human eosinophil peroxidase. The ester with Asp-93 is only partially formed in vivo

The covalent heme attachment has been extensively studied by spectroscopic methods in myeloperoxidase and lactoperoxidase (LPO) but not in eosinophil peroxidase (EPO). We show that heme linkage to the heavy chain is invariably present, whereas heme linkage to the light chain of EPO is present in less than one-third of EPO molecules. Mass analysis of isolated heme bispeptides supports the hypothesis of a heme b linked through two esters to the polypeptide. Mass analysis of heme monopeptides reveals that >90% have a nonderivatized methyl group at the position of the light chain linkage. Apparently, an ester had not been formed during biosynthesis. The light chain linkage could be formed by incubation with hydrogen peroxide, in accordance with a recent hypothesis of autocatalytic heme attachment based on studies with LPO (DePillis, G. D., Ozaki, S., Kuo, J. M., Maltby, D. A., and Ortiz de Montellano P. R. (1997) J. Biol. Chem. 272, 8857-8860). By sequence analysis of isolated heme peptides after aminolysis, we unambiguously identified the acidic residues, Asp-93 of the light chain and Glu-241 of the heavy chain, that form esters with the heme group. This is the first biochemical support for ester linkage to two specific residues in eosinophil peroxidase. From a parallel study with LPO, we show that Asp-125 and Glu-275 are engaged in ester linkage. The species with a nonderivatized methyl group was not found among LPO peptides.

Resonance Raman microspectroscopy of myeloperoxidase and cytochrome b558 in human neutrophilic granulocytes

With (resonance) Raman microscospectroscopy, it is possible to investigate the chemical constitution of a very small volume (0.5 fl) in a living cell. We have measured resonance Raman spectra in the cytoplasm of living normal, myeloperoxidase (MPO)-deficient, and cytochrome b558-deficient neutrophils and in isolated specific and azurophilic granule fractions, using an excitation wavelength of 413.1 nm. Similar experiments were performed after reduction of the redox centers by the addition of sodium dithionite. The specific and azurophilic granules in both redox states appeared to have clearly distinguishable Raman spectra when exciting at a wavelength of 413.1 nm. The azurophilic granules and the cytochrome b558-deficient neutrophils showed Raman spectra similar to that of the isolated MPO. The spectra of the specific granules and the MPO-deficient neutrophils corresponded very well to published cytochrome b558 spectra. The resonance Raman spectrum of the cytoplasmic region of normal neutrophilic granulocytes could be fitted with a combination of the spectra of the specific and azurophilic granules, which shows that the Raman signal of neutrophilic granulocytes mainly originates from MPO and cytochrome b558, at an excitation wavelength of 413.1 nm.

Lipid structure of cytotoxic granules in living human killer T lymphocytes studied by Raman microspectroscopy

The structures of cytotoxic granules in interleukin-2-activated human killer T lymphocytes have been investigated by Raman microspectroscopy at a single cell level. The Raman spectra of granules share a common feature that lipid Raman bands are much stronger than the Raman bands due to protein, indicating that one of the main components of the granule is lipid. To analyze the lipid structures of individual granules, relationships between Raman spectra and structures have been examined for a series of triacylgycerols with varied degrees of acyl chain unsaturation. Analysis based on the relationships shows that the granulous lipid is characterized by a high content of cis C=C bond, which ranges from about 1.5 C=C bonds per acyl chain in isolated minor granules and to about 2.2 C=C bonds in clustering major granules. The highly unsaturated lipid of major cytotoxic granules is in sharp contrast to the moderately unsaturated (about one C=C bond per acyl chain) plasma membrane lipid. The large difference in lipid unsaturation between the granule and plasma membrane may have relevance to the role of granulous lipid in packaging cytotoxic proteins inside the granule and preventing them from attacking the killer lymphocyte itself.