SEARCH · PubMed Health

Results for “Spectroscopy, Near-Infrared”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14Linked to original sources

PubMed1994

The use of near-infrared charge-transfer transitions of low-spin ferric chlorins in axial ligand assignment.

The near-infrared magnetic circular dichroism spectra of some low-spin derivatives of ferric-octaethylchlorin substituted myoglobin have been recorded at cryogenic temperatures. The spectra, which include some of the lowest energy charge-transfer transitions ever observed for hemes, are clearly dependent upon the nature of the axial ligands present. While the results indicate that such spectra may have some practical utility in axial ligand assignment, as is now quite common practice for iron-porphyrin systems, there are some severe practical limitations to this protocol documented in the case of iron-chlorins.

Apoproteins↗

PubMed1994

Structural and spectral characterisation of the antenna complexes of Rhodocyclus gelatinosus. Indications of a hairpin-like-arranged antenna apoprotein with an unusually high alanine content.

The core antenna/reaction-centre complex RC-B875 and the peripheral antenna complex B800-850 of the two strains DSM 149 and DSM 151 of the purple non-sulphur bacterium Rhodocyclus gelatinosus have been isolated from photosynthetic membranes by means of lauryl-N,N-dimethyl-amineoxide as a detergent and subsequent sucrose-gradient centrifugation. The two complexes were characterised spectroscopically by absorption and circular dichroism (CD) spectroscopy at room temperature. CD measurements revealed very weak signals for the core antenna B875 whereas for the peripheral antenna B800-850, a strong biphasic CD signal was observed, attributable to the B850 pigments. There is apparently no CD signal present for the B800 pigments. The core and the peripheral antenna complex are built up by a distinct alpha/beta-polypeptide pair. The pigment/protein ratio in the peripheral antenna complex is 3 bacteriochlorophyll/(alpha/beta)-polypeptide pair. The amino acid sequences of the alpha and beta polypeptides of both complexes from the two strains of Rc. gelatinosus were established by automated Edman degradation, chemical and enzymic digestion, amino acid composition analyses and carboxypeptidase digestion. In the case of the beta polypeptides, the amino acid sequence determination was confirmed by ion-spray MS of the isolated antenna apoproteins. The inter-strain (DSM 149 and 151) positional identity between the equivalent apoproteins is extremely large and varies in the range 90-100%. The B875-beta polypeptide from Rc. gelatinosus exhibits shortened C-termini, as detected for the analogous antenna apoproteins of Rhodobacter sphaeroides and Rhodobacter capsulatus, which can be correlated with weak core antenna near-infrared CD signals. However, the B800-850-alpha polypeptide of Rc. gelatinosus, with 71 amino acids, exhibits an extended C-terminal portion indicative of the formation of a second transmembrane domain, which so far has not been observed for bacterial antenna apoproteins. This part of the molecule is extremely rich in alanine and proline residues. All the sequenced antenna apoproteins of Rc. gelatinosus exhibit a characteristic membrane-buried histidine which is thought to ligate the B875 or the B850 pigments. In the B800-850-beta apoprotein, a second, so far beta-antenna-apoprotein-specific histidine, is replaced by a glutamine residue. A careful inspection of the determined antenna structures of Rc. gelatinosus revealed some remarkable structural similarities within presumed cofactor-binding sites of Fe-S-type-reaction-centre apoproteins, indicating possible basic structural motifs for complexing bacteriochlorophyll molecules.

Alanine↗

PubMed1988

The effect of hyperbaric oxygen on cerebral hemoglobin oxygenation and dissociation rate of carboxyhemoglobin in anesthetized rats: spectroscopic approach.

By measuring near-infrared transmittance spectra, we examined the effect of HBO on cerebral Hb oxygenation in normal and ischemic brain in the anesthetized rat. The oxygenation state of Hb was around 80% in the rat brain under 1 ATA air breathing. HBO did not induce further cerebral Hb oxygenation above 2 ATA in control animals but improved tissue oxygenation in the ischemic brains. The oxidation-reduction state of cyt. aa3 in the normal brain was not affected by HBO. In the ischemic brain, however, HBO prevented ischemia-induced reduction of cyt. aa3. Non-invasive optical monitoring of COHb with visible reflectance spectrophotometry was also examined. HBO markedly accelerated dissociation of COHb. Tight correlation was found between the optical signal and COHb content determined from blood samples. These results demonstrated the usefulness of optical monitoring in vivo under hyperbaric conditions.

Anaerobiosis↗

PubMed1996

Conversion of the spin state of the manganese complex in photosystem II induced by near-infrared light.

The manganese complex (Mn4) which is responsible for water oxidation in photosystem II is EPR detectable in the S2 state, one of the five redox states of the enzyme cycle. The S2 state is observable at 10 K either as a multiline signal (spin 1/2) or as a signal at g = 4.1 (spin 3/2 or spin 5/2). It is shown here that at around 150 K the state responsible for the multiline signal is converted to that responsible for the g = 4.1 signal upon the absorption of infrared light. This conversion is fully reversible at 200 K. The action spectrum of this conversion has its maximum at 820 nm (12 200 cm-1) and is similar to the intervalence charge transfer band in di-mu-oxo-(MnIIIMnIV) model systems. It is suggested that the conversion of the multiline signal to the g = 4.1 signal results from absorption of infrared light by the Mn cluster itself, resulting in electron transfer from MnIII to MnIV. The g = 4.1 signal is thus proposed to arise from a state which differs from that which gives rise to the multiline signal only in terms of this change in its valence distribution. The near-infrared light effect was observed in the S2 state of Sr(2+)-reconstituted photosystem II and in Ca(2+)-depleted, EGTA (or citrate-)-treated photosystem II but not in ammonia-treated photosystem II. Earlier results in the literature which showed that the g = 4.1 state was preferentially formed by illumination at 130 K are reinterpreted as being the result of two photochemical events: the first being photosynthetic charge separation resulting in an S2 state which gives rise to the multiline signal and the second being the conversion of this state to the g = 4.1 state due to the simultaneous and inadvertent presence of 820 nm light in the broad-band illumination given. There is therefore no reason to consider the state responsible for the g = 4.1 signal as a precursor of that which gives rise to the multiline signal.

Ammonia↗

PubMed1992

Thiobacillus ferrooxidans cytochrome c oxidase: purification, and molecular and enzymatic features.

Cytochrome c oxidase from Thiobacillus ferrooxidans was purified to homogeneity and some of its properties were studied. The oxidase was solubilized with n-octyl-beta-D-thioglucoside (OTG) under acidic conditions (pH 4.0) and purified by one step of ion-exchange chromatography with a CM-Toyopearl column. The absorption spectrum of the oxidase showed peaks at 420 and 595 nm in the oxidized form and at 440 and 595 nm in the reduced form. Its CO compound showed a novel absorption spectrum; a double-peaked gamma band appeared at 429 and 438 nm. The oxidase seemed to have CuA-like copper atom from its ESR and near-infrared spectra. The oxidase molecule consisted of three polypeptides with molecular weights of 53,000, 22,000, and 17,000, respectively, as estimated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The molecular weight of the enzyme in a solution containing detergents was estimated to be 169,000 on the basis of the results obtained by gel filtration, while the molecular weight per heme alpha was estimated to be 83,700. The copper content of the oxidase was 1.01 g atom per mol of heme alpha. Therefore, the cytochrome seemed to contain one molecule of heme alpha and one atom of copper in the minimal structural unit consisting of one molecule each of the three subunits, and to occur as a dimer of the unit in the solution. The oxidase oxidized ferrocytochrome c-552 of the bacterium, and the optimal pH of the reaction was 3.5.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Fractionation↗

PubMed1991

Spectroscopic studies of cobalt and nickel substituted rubredoxin and desulforedoxin.

The single iron site of rubredoxin was replaced by nickel and cobalt. The near-infrared/visible/UV spectra of these metal derivatives show ligand-field transitions and charge-transfer bands which closely resemble those of simple tetrathiolate complexes, indicating a tetrahedral arrangement of the sulfur cysteinyl ligands around the metal core. The 1H NMR spectra of the nickel and cobalt derivatives reveal extremely low-field contact shifted resonances of one proton intensity assigned to beta-CH2 and alpha-CH cysteinyl protons. Other well resolved resonances shifted out of the main protein spectral envelope are also observed and probably arise from contact plus pseudocontact shift mechanisms. Rubredoxins from different sulfate reducers were metal substituted and assignments of aliphatic protons are tentatively proposed, taking advantage of the amino acid sequence homologies. The present data is promising in terms of structural analysis of the coordination sphere of the metal core. It was also shown that replacement of the iron atom of desulforedoxin, a close analogue of rubredoxin, by cobalt and nickel was possible.

Amino Acid Sequence↗

PubMed1989

The axial ligands of heme in cytochromes: a near-infrared magnetic circular dichroism study of yeast cytochromes c, c1, and b and spinach cytochrome f.

Room temperature near-infrared magnetic circular dichroism and low-temperature electron paramagnetic resonance measurements have been used to characterize the ligands of the heme iron in mitochondrial cytochromes c, c1, and b and in cytochrome f of the photosynthetic electron transport chain. The MCD data show that methionine is the sixth ligand of the heme of oxidized yeast cytochrome c1; the identify of this residue is inferred to be the single conserved methionine identified from a partial alignment of the available cytochrome c1 amino acid sequences. A different residue, which is most likely lysine, is the sixth heme ligand in oxidized spinach cytochrome f. The data for oxidized yeast cytochrome b are consistent with bis-histidine coordination of both hemes although the possibility that one of the hemes is ligated by histidine and lysine cannot be rigorously excluded. The neutral and alkaline forms of oxidized yeast cytochrome c have spectroscopic properties very similar to those of the horse heart proteins, and thus, by analogy, the sixth ligands are methionine and lysine, respectively.

Amino Acid Sequence↗

PubMed1985

Chemical modification of the CuA center in cytochrome c oxidase by sodium p-(hydroxymercuri)benzoate.

Cytochrome c oxidase contains a copper ion electron-transfer site, CuA, which has previously been found to be unreactive with externally added reagents under conditions in which the protein remains structurally intact. We have studied the reaction of cytochrome oxidase with sodium p-(hydroxymercuri) benzoate (pHMB) and found that the reaction proceeds, under appropriate conditions, to give an excellent yield of a particular derivative of the CuA center that has electron paramagnetic resonance and near-infrared absorption spectroscopic properties which are distinctly different from those of the unmodified center. Spectroscopic and chemical characterization of the other metal ion sites of the enzyme reveals little or no effect of the pHMB modification on the structures of and reactions at those sites. Of particular interest is the observation that the modified enzyme still displays a substantial fraction of the native steady-state activity of electron transfer from ferrocytochrome c to O2. Although the modified copper center retains the ability to receive electrons from the powerful reductant Na2S2O4 and to transfer electrons to O2, it is not significantly reduced when the enzyme is treated with milder (higher potential) reductants such as NADH/phenazine methosulfate or the physiological substrate ferrocytochrome c. CuA exhibits many spectroscopic and chemical properties which make it highly atypical of cuproprotein active sites; the singular nature of this site has prompted speculation about the importance of the structural peculiarities of this metal ion center in the catalytic cycle of the enzyme. In this work, we demonstrate that the unusual features of this site are not prerequisites for competent catalysis of electron transfer and O2 reduction by the enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1996

The antenna complexes of the purple non-sulfur photosynthetic bacterium Rhodocyclus tenuis. Structural and spectral characterization.

The photoreceptor complex (B885-RC) and the peripheral antenna complex (B800-860) were isolated from photosynthetic membranes of the purple non-sulfur bacterium Rhodocyclus tenuis DSM 109 using a detergent combination of Deriphate-160 and octyl glucoside and subsequent linear sucrose gradient centrifugation. The two complexes were characterized by room-temperature absorption, circular dichroism and fluorescence spectroscopy. The B800-860 complex has a more red-shifted B860 absorbance band. The alpha,beta-polypeptides were purified with a reverse-phase HPLC system and resolved at a ratio of 1:1 in the B800-860 complex and at an overall ratio of 1:1 for the B885-RC complex. The complete amino acid sequences of the alpha and beta polypeptides of the B800-860 and B885-RC complexes were determined by micro-sequencing analysis and mass spectrometry. The B800-860-alpha polypeptide possesses an identical N-terminal domain (the first 15 residues) to Rhodobacter sphaeroides B800-850-alpha polypeptide. The central hydrophobic and C-terminal domains of the B800-860-alpha,beta polypeptides show a number of B870/880-like structural elements in which, of special interest, is the WWSEF cluster in the C-terminal domain of the B800-860-alpha polypeptide which is very similar to the WWEF cluster in the same region of Rhodopseudomonas viridis B1015-alpha polypeptide. The more red-shifted absorption characteristic of the 860-nm bacteriochlorophylls could most probably be related to the B870/880-like polypeptide features in the central hydrophobic domains and the C-terminal domains of the B800-860-alpha,beta polypeptides. The hydropathy plot of the B800-860-alpha polypeptide exhibits an extended C-terminal hydrophobic segment indicative of a second membrane-contacting domain, which has not been found in the antenna polypeptides of the purple bacteria with intracytoplasmic membranes. Further sequence analysis revealed the existence of multiple forms of the B885-alpha,beta polypeptides, the B885-alpha 1,alpha 2 polypeptides, and the B885-beta 1,beta 2 polypeptides. The B885-Alpha 2 polypeptide shows an identical sequence to the B885-alpha 1 polypeptide, but it is 12 amino acid residues shorter than the B885-alpha 1 polypeptide at the C-terminal. The two species of the B885-beta polypeptides were identified as an identical sequence with only one amino acid residue variation at sequence position 34, where the B885-beta 1 has a valine residue and the B885-beta 2 polypeptide an isoleucine residue. The possible correlation between the intensity of the near-infrared circular dichroic signal and the specific structural features of the alpha and beta core antenna polypeptides is also discussed.

Amino Acid Sequence↗

PubMed1994

FT-IR and near-infrared FT-Raman studies of the secondary structure of insulinotropin in the solid state: alpha-helix to beta-sheet conversion induced by phenol and/or by high shear force.

Insulinotropin (glucagon-like peptide I) is a peptide containing 31 amino acid residues. It stimulates the secretion of the hormone insulin. The solubility of this peptide is highly dependent on its environment and the treatment that it has undergone. For instance, synthetic insulinotropin is highly soluble in neutral phosphate-buffered saline (1 mg/mL). However, the application of shear force by stirring renders it extremely insoluble (1 micrograms/mL). This property may be explained in terms of a change in peptide secondary structure with no alteration in primary structure. In order to understand this phenomenon, FT-IR and near-IR FT-Raman were employed to examine four samples prepared under different experimental conditions. It was found that solubility decreases as the alpha-helix is converted to an antiparallel beta-sheet structure.

Amino Acid Sequence↗

PubMed1996

Axial heme ligation in the cytochrome bc1 complexes of mitochondrial and photosynthetic membranes. A near-infrared magnetic circular dichroism and electron paramagnetic resonance study.

The combination of EPR and low-temperature near-IR magnetic circular dichroism spectroscopies have been used to investigate the axial ligation of the cytochromes in the cytochrome bc1 complexes from bovine heart mitochondria, Rhodobacter capsulatus, Rhodobacter sphaeroides, and Rhodospirillum rubrum, and the purified cytochromes c1 from bovine heart mitochondria, Rb. capsulatus and Rb. sphaeroides. The possibility of axial ligation of cytochrome c1 by the amino terminus of the polypeptide was also assessed by acetylating the N-terminus of Rb. capsulatus cytochrome c1 and comparing the properties of the acetylated and unmodified samples. The results are consistent with bis-histidine axial ligation for the high- and low-potential b-type cytochromes and histidine/methionine axial ligation for the c1-type cytochrome in the intact cytochrome bc1 complexes. Purified samples of cytochrome c1 are mixtures of two forms, one with histidine/methionine and the other with bis-histidine axial ligation. The form with bis-histidine axial ligation is also assembled in the M183L mutant of the Rb. capsulatus cyt bc1 complex in which the methionine residue coordinating cyt c1 is replaced by a leucine. The bis-histidine form appears to be an artifact of dissociation of cytochrome c1 from the cytochrome bc1 complex and is greatly enhanced particularly in the bacterial cytochromes c1 by sample handling and the addition of 50% (v/v) ethylene glycol or glycerol.

Amino Acid Sequence↗

PubMed1991

Rapid verification of identity and content of drug formulations using mid-infrared spectroscopy.

A general method for the rapid verification of both identity and content of complete solid drug formulations has been devised. Infrared spectra for the samples were recorded using the diffuse reflectance technique, and specially written software was employed to identify the type of formulation and level of active ingredient. This software was devised to ensure reliable use when applied by those with minimal operator skills. Three differing drug tablet formulations containing simvastatin, enalapril maleate and lovastatin, as well as a capsule formulation containing finastride were studied. Adequate precision was obtained to reliably verify drug dosage levels. Near-infrared (NIR) and mid-infrared (MIR) spectrometers were evaluated for use with the method. The MIR instrument allowed sufficient resolution and spectral/structural selectivity to reliably verify correctness of either of two near derivative drugs necessarily present in the same clinical study. Drug tablet and capsule dosage levels tested ranged from 0.2 to 40 mg of drug. Approximately 1% (w/w) of the drug in the formulation was the minimum amount determined. Parameters affecting method ruggedness in routine use were optimized. Experimental addition of an extraneous material to a simvastatin formulation was easily detected and flagged by the routine test procedure. Subsequent data retrieval and searching against spectral libraries was used to demonstrate identification of the additive.

Anticholesteremic Agents↗

PubMed1993

Near-infrared spectroscopic measurement of glucose in a protein matrix.

A method is described for measuring clinically relevant levels of glucose in a protein matrix by near-infrared (near-IR) absorption spectroscopy. Results from an initial screening of major blood constituents identify protein as a major potential interference to the near-IR measurement of glucose in blood. The interference by protein is caused by relatively high concentrations coupled with strong near-IR absorption bands between 5000 and 4000 cm-1 (2.0-2.5 microns). Calibration models based on a simple univariate calibration procedure are not capable of providing accurate glucose concentrations from an independent set of prediction spectra. By use of the multivariate technique of partial least squares (PLS) regression, glucose concentrations can be determined with a 0.35 mM (6.3 mg/dL) standard error of prediction. The spectral range for this calibration model extends from 4600 to 4200 cm-1, and the optimum number of PLS factors is 14. In addition, calibration models based on a combination of digital Fourier filtering and PLS regression have been constructed and evaluated. Superior calibration models are obtained by using a preprocessing digital filtering step to remove spectral features not associated with glucose. The best overall calibration model was obtained by using a Gaussian-shaped Fourier filter defined by a mean position of 0.03f and standard deviation of 0.007f coupled with a 12-factor PLS regression computed over the spectral range from 4600 to 4200 cm-1. This model provided a standard error of prediction of 0.24 mM (4.3 mg/dL) for an independent set of prediction spectra.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Glucose↗

PubMed1995

Near-infrared measurement of relative and absolute humidity through detection of water adsorbed on a silica gel layer.

Near-IR spectroscopy is especially well suited to moisture determination because of the relatively high absorptivity of water compared to most other substances. In the present work, near-IR diffuse-transmittance spectroscopy is applied to the measurement of humidity via observation of adsorbed water on a high-performance thin-layer chromatography silica gel plate. The adsorbed water is detected through both ordinary absorption of radiation by water molecules and the increased scattering of near-IR radiation by the silica gel as it adsorbs more water. This technique shows promise as a highly accurate and sensitive humidity sensor with a time constant of less than 1 min. The addition of inorganic salts to the silica gel layer is shown to increase the response to water vapor. However, it also increases the time constant of the sensor. A miniature humidity sensor using a commercially available near-IR transmissive switch is also demonstrated. Possible interferences and hysteresis effects are investigated.

Adsorption↗

PubMed1996

Near-infrared spectroscopic measurement of physiological glucose levels in variable matrices of protein and triglycerides.

Selective calibration models are generated for glucose over the 1-20 nM concentration range by use of partial least-squares regression analysis of near-infrared spectra from 5000 to 4000 cm-1. Two spectral data sets are used to simulate triglyceride and protein variations in clinical samples. Triacetin is used in one data set to simulate variations in triglyceride levels, and bovine serum albumin (BSA) is used in the second data set to simulate variations in blood protein levels. Although these matrix components possess strong absorption bands that overlap and overshadow the absorption bands of glucose, successful calibration models can be generated with no evidence of prediction bias caused by the different levels of the matrix components. Furthermore, the benefits of using digital Fourier filtering as a preprocessing step are evaluated in terms of calibration performance. The resulting calibration models provide standard errors of prediction of 0.5 and 0.2 mM in triacetin and BSA matrices, respectively. Accurate glucose predictions are demonstrated from spectra that correspond to protein concentrations not present in the calibration data set. Lastly, digital Fourier filtering alone is shown to have only limited ability to isolate glucose signals from those of BSA and triacetin due to similarities in the widths of the absorption bands of the three species.

Animals↗

PubMed1995

FT-IR and near-infrared FT-Raman study of aggregation of bacteriochlorophyll c in solutions: evidence for involvement of the ester group in the aggregation.

Ultraviolet-visible (UV-Vis) absorption, Fourier-transform infrared (FT-IR), and near-infrared (NIR)-excited FT-Raman spectra have been measured for bacteriochlorophyll c (BChl-c) in acetone, tetrahydrofuran (THF), pyridine-d5, carbon disulfide (CS2), and water-saturated carbon tetrachloride (CCl4) to investigate its aggregation in vitro. The UV-Vis absorption spectra can be classified into two groups. Group I (acetone, THF, and pyridine-d5 solutions) gives a spectrum with a Qy band around 665 nm while group II (CS2 and water-saturated CCl4 solutions) shows a spectrum typical of BChl-c aggregates with a broader red-shifted Qy band. All the NIR-FT-Raman spectra, which are preresonant with the Qy band, are very close to those of chlorophyll a (Chl-a) measured in the corresponding solutions. Bands due to a C = O stretching mode of free and strongly hydrogen-bonded 13(1)-keto carbonyl groups appear near 1685 and 1645 cm-1, respectively. In contrast to the FT-Raman spectra, FT-IR spectra of the pyridine-d5 solution and group II are largely different from those of Chl-a in the corresponding solutions, suggesting that BChl-c forms quite different types of aggregates. It is clear from the IR spectra that the ester carbonyl group plays an important role in the aggregation for the pyridine-d5 and group II solutions. Of particular note is that bands due to C = O stretching modes of the ester group are observed at 1733, 1719, and 1705 cm-1 in the spectrum of BChl-c in water-saturated CCl4.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteria↗

PubMed1982

Infrared spectroscopy of photodissociated carboxymyoglobin at low temperatures.

We have studied the infrared spectra of the bound and photodissociated states of Mb-12CO and Mb-13CO from 5.2 to 300 K. The absorbance peaks seen between 1800 and 2200 cm-1 correspond to CO stretching vibrations. In the bound state of Mb-12CO, the known lines A0 at 1969, A1 at 1945, and A2 at 1927 cm-1, have center frequencies, widths, and absorbances that are independent of temperature between 5.2 and 160 K. Above 160 K, A2 gradually shifts to 1933 cm-1. The low-temperature photodissociated state (Mb) shows three lines (B0, B1, B2) at 2144, 2131, and 2119 cm-1 for 12CO. The absorbances of the three lines depend on temperature. B0 is tentatively assigned to free CO in the heme pocket and B1 and B2, to CO weakly bound to the heme or heme pocket wall. The data are consistent with a model in which photodissociation of MbCO leads to B1 and B2. B2 decays thermally to B1 above 13 K; rebinding to A occurs from B1. The barriers between B2 and B1 and between B1 and A are described by activation enthalpy spectra. Heme and the central metal atom in state Mb have near-infrared, EPR, and Mössbauer spectra that differ slightly from those of deoxyMb. The observation of essentially free CO in state B implies that the difference between Mb and deoxyMb is not due to an interaction of the flashed-off ligand with the protein but is caused by an incomplete relaxation of the protein structure at low temperatures.

Animals↗

PubMed1984

X-ray diffraction studies on chromatophore membrane from photosynthetic bacteria. II. Comparison of diffraction patterns of photosynthetic units from various purple bacteria.

Comparative X-ray diffraction studies, in conjunction with infrared absorption spectroscopy, were performed on chromatophores isolated from various purple photosynthetic bacteria in order to achieve a better understanding of the molecular structure of the photosynthetic unit. Purple non-sulfur bacteria used were Rhodospirillum rubrum, Rhodospirillum molischianum, Rhodopseudomonas sphaeroides, and Rhodopseudomonas palustris. Chromatophores of Chromatium vinosum, as a typical example of purple sulfur bacteria, were also investigated. The results were as follows. Distinct equatorial X-ray diffraction patterns were obtained from chromatophores of all the bacteria examined. They showed diffuse, continuous diffraction patterns having several maxima, and the patterns are evidently distinguished from those of either crystalline or amorphous material. The pattern indicates that the photosynthetic unit in the chromatophore has a highly organized molecular structure in the plane of the membrane. Bacteria whose major photosynthetic pigment is bacteriochlorophyll alpha can be categorized in three groups from the viewpoint of near infrared absorption spectra. X-ray diffraction patterns are also grouped accordingly, although the differences are minimal and the patterns display common features. In other words, the bacteriochlorophyll forms, which are bacteriochlorophyll-protein complexes exhibiting different near-infrared absorption spectra, show different X-ray patterns: the molecular structure of photosynthetic units is closely related to the state of pigment in each complex, although the "X-ray" molecular structure is mainly concerned with the arrangement of constituent protein molecules at the present resolution, whereas the "spectroscopic" structure reflects the local environment of pigment.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial Chromatophores↗