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Biomedical subjects

H A Frank

Publications and source records attributed to H A Frank.

At least 19 recordsLinked to original sources
PubMed1992

13C magic angle spinning NMR evidence for a 15,15'-cis configuration of the spheroidene in the Rhodobacter sphaeroides photosynthetic reaction center.

The photosynthetic reaction center of Rhodobacter sphaeroides 2.4.1 contains one carotenoid that protects the protein complex against photodestruction. The structure around the central (15,15') double bond of the bound spheroidene carotenoid was investigated with low-temperature magic angle spinning 13C NMR, which allows an in situ characterization of the configuration of the central double bond in the carotenoid. Carotenoidless reaction centers of R. sphaeroides R26 were reconstituted with spheroidene specifically labeled at the C-14' or C-15' position, and the signals from the labels were separated from the natural abundance background using 13C MAS NMR difference spectroscopy. The resonances shift 5.2 and 3.8 ppm upfield upon incorporation in the protein complex, similar to the 5.6 and 4.4 ppm upfield shift occurring in the model compound beta-carotene upon trans to 15,15'-cis isomerization. Hence the MAS NMR favors a cis configuration, as opposed to the trans configuration deduced from X-ray data.

Carbon Isotopes↗
PubMed1992

Qy-excitation resonance Raman scattering from the special pair in Rhodobacter sphaeroides reaction centers. Implications for primary charge separation.

Qy-excitation resonance Raman (RR) spectra are reported for reaction centers (RCs) from Rhodobacter sphaeroides 2.4.1. The RR spectra were acquired for both chemically reduced and oxidized RCs at 25 and 201 K by using a variety of excitation wavelengths in the range 800-920 nm. This range spans the Qy absorption bands of the special pair (P) and the accessory bacteriochlorophylls (BChls). The RR studies indicate that both P and the accessory BChls exhibit rich RR spectra in the 30-1800-cm-1 region. For both types of pigments, at least 20 bands are observed in the 30-750-cm-1 range. Although the frequencies of the modes of P and the accessory BChls are different, it is possible to make one-to-one correlations of the bands observed for the two types of pigments. This result suggests that the vibronically active low-frequency modes of P are derived from monomer-like vibrations (although they may be coupled monomer-like modes) rather than being vibrations resulting from the additional degrees of freedom present in the dimer. A plausible set of vibrational assignments for the low-frequency modes of both P and the accessory BChls is proposed on the basis of a semiempirical normal coordinate calculation. Comparison of the RR intensities of the low-frequency modes of P with those of the analogous modes of the accessory BChls indicates that the intensities of the modes of the former pigments are considerably larger than those of the latter. Collectively, the spectral data indicate that a large number of low-frequency modes of P are strongly coupled to the Qy electronic transition.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxidation-Reduction↗
PubMed1992

Low-lying electronic states of carotenoids.

Four all-trans carotenoids, spheroidene, 3,4-dihydrospheroidene, 3,4,5,6-tetrahydrospheroidene, and 3,4,7,8-tetrahydrospheroidene, have been purified using HPLC techniques and analyzed using absorption, fluorescence and fluorescence excitation spectroscopy of room temperature solutions. This series of molecules, for which the extent of pi-electron conjugation decreases from 10 to seven carbon-carbon double bonds, exhibits a systematic crossover from S2----S0 (1(1)Bu----1(1)Ag) to S1----S0 (2(1)Ag----1(1)Ag) emission with decreasing chain length. Extrapolation of the S1----S0 transition energies indicates that the 2(1)Ag states of longer carotenoids have considerably lower energies than previously thought. The energies of the S1 states of spheroidenes and other long carotenoids are correlated with the S1 energies of their chlorophyll partners in antenna complexes of photosynthetic systems. Implications for energy transfer in photosynthetic antenna are discussed.

Carotenoids↗
PubMed1991

Femtosecond energy-transfer processes in the B800-850 light-harvesting complex of Rhodobacter sphaeroides 2.4.1.

The B800-to-B850 energy transfer time in the purified B800-850 light-harvesting complex of Rhodobacter sphaeroides 2.4.1 is determined to be 0.7 ps at room temperature. The electronic state dynamics of the principal carotenoid of this species, spheroidene, are examined, both in vivo and in vitro, by direct femtosecond time-resolved experiments and by fluorescence emission yield studies. Evidence is presented which suggests that carotenoid-to-bacteriochlorophyll energy transfer may occur directly from the initially excited carotenoid S2 state, as well as from the carotenoid S1 state. Further support for this conjecture is obtained from calculations of energy transfer rates from the carotenoid S2 state. Previous measurements of in vivo carotenoid and B800 dynamics are discussed in light of the new results, and currently unresolved issues are described.

Bacteriochlorophylls↗
PubMed1991

Low temperature polarized absorption microspectroscopy of single crystals of the reaction center from Rhodobacter sphaeroides wild type strain 2.4.1.

The absorbance and polarized absorbance spectra of single crystals of the reaction center complex isolated from Rhodobacter sphaeroides wild type strain 2.4.1 have been measured at 85 K. The crystals of the complex were obtained by the vapor diffusion technique. The spectroscopic experiments on the crystals were performed using an optical microspectrometer featuring a custom-built, liquid N2-flowing cold stage, the details of which are presented herein. These data demonstrate the feasibility of conducting optical spectroscopic experiments at cryogenic temperatures on single crystals of photosynthetic pigment-protein complexes.

Bacteriochlorophylls↗
PubMed1991

Dialysis of plasma soluble lipofuscins in patients with end-stage renal failure.

Fluorescence spectrophotometry demonstrates that the levels of plasma soluble lipofuscins (SL) in patients with end-stage renal failure, undergoing continuous ambulatory peritoneal dialysis (CAPD) or haemodialysis (HD), remain significantly higher than in normal subjects. Plasma samples from these patients show the presence of SL generated from 3-hydroxy-anthranilic acid [excitation (ex) at approximately 324 nm and emission (em) at approximately 413 nm] and of other SL generated from dopa, catecholamines, 3-hydroxykynurenine and from structurally related precursors (ex at approximately 345 nm, em at approximately 445 nm). These precursors form the melanin components, which are approximately 3 wt % of SL. The fluorescence of SL appears to originate mainly from the melanin components. Peaks and shoulders at these wavelengths are found in the spectra of all dialysates. Based on intensity measurements at 413 nm and 445 nm, the weekly clearance rates with HD are in general greater than those with CAPD. The saponified cellulose ester membrane used in HD passes only lower-molecular-weight SL and/or components of SL. After HD, the greatest reductions in plasma intensities are found at approximately 324 nm and approximately 413 nm. The clearance rates (l/week) are always greater at 413 nm [means HD: 18.47 +/- 4.44 standard deviation (SD), n = 8; CAPD: 12.50 +/- 2.47, n = 4] than at 445 nm (HD: 10.94 +/- 3.86; CAPD: 7.95 +/- 1.75) both with HD and CAPD. In CAPD, the membrane also permits the passage of large amounts of albumin and other high-molecular-weight substances.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Temperature-dependent conformational changes in the bacteriopheophytins of Rhodobacter sphaeroides reaction centers.

Resonance Raman (RR) spectra are reported for the photosynthetic reaction center (RC) protein from Rhodobacter sphaeroides 2.4.1. The spectra were obtained with a variety of excitation wavelengths, spanning the UV, violet, and yellow-green regions of the absorption spectrum, and at a number of temperatures ranging from 30 to 270 K. The RR data indicate that the frequencies of certain vibrational modes of the bacteriochlorin pigments in the RC shift with temperature. These shifts are reversible and do not depend on external factors such as solvent or detergent. The acetyl carbonyl bands exhibit the largest shifts with temperature. These shifts are attributed to thermal effects involving the torsional vibrations of the acetyl groups of several (or all) of the bacteriochlorins rather than to specific pigment-protein interactions. The frequency of the structure-sensitive skeletal mode near 1610 cm-1 of one of the two bacteriopheophytins (BPhs) in the RC is also sensitive to temperature. In contrast, no temperature sensitivity is observed for the analogous modes of the bacteriochlorophylls or other BPhs. Over the range 160-100 K, the skeletal mode of the BPh upshifts by approximately 4 cm-1. This upshift is attributed to a flattening of the macrocycle at low temperatures. It is suggested that the BPh active in the electron-transfer process is the pigment whose structure is temperature dependent. It is further suggested that such structural changes could be responsible in part for the temperature dependence of the electron-transfer rates in photosynthetic RCs.

Bacterial Proteins↗
PubMed1990

Femtosecond dynamics of energy transfer in B800-850 light-harvesting complexes of Rhodobacter sphaeroides.

We report femtosecond transient absorption studies of energy transfer dynamics in the B800-850 light-harvesting complex (LHC) of Rhodobacter sphaeroides 2.4.1. For complexes solubilized in lauryldimethylamine-N-oxide (LDAO), the carotenoid to bacteriochlorophyll (Bchl) B800 and carotenoid to Bchl B850 energy transfer times are 0.34 and 0.20 ps, respectively. The B800 to B850 energy transfer time is 2.5 ps. For complexes treated with lithium dodecyl sulfate (LDS), a carotenoid to B850 energy transfer time of less than or equal to 0.2 ps is seen, and a portion of the total carotenoid population is decoupled from Bchl. In both LDAO-solubilized and LDS-treated complexes an intensity-dependent picosecond decay component of the excited B850 population is ascribed to excitation annihilation within minimal units of the LHC.

Bacteriochlorophylls↗
PubMed1989

Monomeric bacteriochlorophyll is required for the triplet energy transfer between the primary donor and the carotenoid in photosynthetic bacterial reaction centers.

Reaction centers from the carotenoidless mutant Rb. sphaeroides R26 were treated with sodium borohydride which is known to remove one of the accessory monomeric bacteriochlorophylls (BB). Subsequently, the carotenoid, spheroidene, was incorporated into the modified reaction centers. It is demonstrated by optical absorption and circular dichroism experiments that spheroidene, reconstituted into the sodium borohydride-treated Rb. sphaeroides R26 reaction centers, is bound in a single site, in the same environment and with the same structure as spheroidene reconstituted into untreated (native) Rb. sphaeroides R26 reaction centers. Transient optical and electron spin resonance spectroscopic data indicate that unless the accessory BB is present, the primary donor-to-carotenoid triplet energy transfer reaction is inhibited. These observations provide direct evidence for the involvement of the accessory BB in the triplet energy transfer pathway.

Bacterial Proteins↗
PubMed1989

Electron transfer reactions in photosystem I following vitamin K1 depletion by ultraviolet irradiation.

Photosystem I preparations were irradiated with UV to destroy vitamin K1 in situ. The depletion of vitamin K1 resulted in inactivation of NADP+ photoreduction and introduction of a approximately 220 ms component in the flash generated P700+ rereduction at room temperature. The photoreduction of the terminal FeS centers FA and FB in control and vitamin K1-depleted preparations at 7 K were comparable. The data confirm that vitamin K1 is functionally implicated in primary electron transfer reactions in PS I at physiological temperature, and that the anomalous results at cryogenic temperature may be explicable in terms of a by-pass of the vitamin K1 acceptor site or heterogeneity introduced into the photosystem by quinone removal.

Chlorophyll↗
PubMed1989

Transient optical spectroscopy of single crystals of the reaction center from Rhodobacter sphaeroides wild-type 2.4.1.

The photoactivity of the crystallized reaction centers from Rhodobacter sphaeroides wild-type strain 2.4.1 has been examined by light-induced absorption spectral changes associated with charge separation and triplet state formation in the reaction center. Upon excitation of a crystal at ambient redox potential, the primary donor 865 nm band bleaches reversibly. The kinetics of its recovery were found to be biphasic with rate constants 11.5 +/- 1.3 s-1 and 0.9 +/- 0.4 s-1 which correspond to lifetimes of 87.0 +/- 9.0 ms and 1.0 +/- 0.7 s, respectively. The ratio of the fast-to-slow component preexponential terms was 3.5 +/- 1.1 suggesting that the majority (78.9 +/- 13.0%) of the reaction centers in the crystals lack the secondary quinone, QB. The addition of sodium ascorbate to the crystals attenuates the 865 nm absorption change, and gives rise to strong carotenoid triplet-triplet absorption changes at 547 nm. These data indicate that the reaction center-bound carotenoid in the crystals is capable of accepting triplet energy from the primary donor triplet.

Bacterial Proteins↗
PubMed1989

Morphological changes in putrefactive anaerobe 3679 (Clostridium sporogenes) induced by sorbate, hydrochloric acid, and nitrite.

Putrefactive anaerobe 3679 (Clostridium sporogenes), a gram-positive bacterium, was examined by light and electron microscopy during normal growth and in a medium containing sorbate (50 mM, pH 6.5), hydrochloric acid (pH of medium adjusted from 7 to 5 with HCl), or nitrite (1 mM, pH 7). During the early exponential growth phase, untreated cells were filamentous and nonseptate, but became septate later and divided when the culture entered the stationary phase. Untreated short and filamentous cells had a double-layered cell wall. Sorbate-treated cells were usually filamentous and nonseptate, but with distorted shapes characterized by numerous bends and bulges. Septation, when present, resulted in minicells. The inner cell wall appeared to be thickened and the outer wall was absent in many areas. Acid-treated cells were similar to sorbate-treated cells but contained septa. Considerable cellular debris was present in the suspension. Nitrite-treated cells were also filamentous, bent, and bulged but the cell wall appeared normal. Considerable cellular debris was also present in suspensions of nitrite-treated cells. Changes in morphology are discussed in relation to possible mechanisms of cell growth regulation and the inhibitory action of sorbate, acid, and nitrite.

Cell Wall↗
PubMed1988

Elevated levels of plasma lipofuscins in patients with chronic renal failure.

The fluorescence excitation and emission spectra observed in plasma from patients with chronic renal failure were reproduced by the generation of soluble lipofuscins in normal plasma samples by incubation with mixtures of L-dopa, dopamine, L-norepinephrine, L-epinephrine, 3-hydroxy-DL-kynurenine and 3-hydroxy-anthranilic acid for 24 h at 37 degrees C. Relative fluorescence intensity measurements consistently showed elevated plasma levels of the soluble lipofuscins in chronic renal failure: the means (n = 27) were 73.9 +/- 33.4 (SD) and 71.1 +/- 14.8 at emissions 413 nm and 445 nm respectively, in contrast to those of normal plasma samples (n = 11), 18.2 +/- 5.3 and 23.1 +/- 5.6. The maximum or shoulder at approximately 413 nm represents soluble lipofuscin that can be generated from 3-hydroxyanthranilic acid and the maximum or shoulder at approximately 445 nm represents soluble lipofuscins derived from the precursors listed above and probably from other related precursors. Gravimetric measurements also showed elevated levels of melanins in the plasma samples of patients with chronic renal failure: 2.72 +/- 0.38 mg/ml (n = 16), as compared to normal values: 1.70 +/- 0.10 mg/ml (n = 6). In individual patients haemodialysis reduced the fluorescence intensities to a range of 65-99% and the melanin levels to a range of 86-99% of the pre-dialysis values.

Adolescent↗
PubMed1987

Crystallization and preliminary X-ray and optical spectroscopic characterization of the photochemical reaction center from Rhodobacter sphaeroides strain 2.4.1.

The photochemical reaction center from Rhodobacter sphaeroides 2.4.1 has been crystallized. The crystals were obtained in a solution of beta-octylglucoside by the vapor diffusion technique using polyethylene glycol 4000 as the precipitant at 22 degrees C. The orthorhombic crystals (space group P2(1)2(1)2(1)) have cell constants a = 142.5 A, b = 136.1 A, c = 78.5 A, and diffract to 3.7 A. The crystals display pronounced linear dichroism in the carotenoid absorption spectral region.

Bacterial Proteins↗
PubMed1987

Near-infrared-excitation resonance Raman spectra of bacterial photosynthetic reaction centers. Implications for path-specific electron transfer.

The first near-infrared (Qy)-excitation resonance Raman spectrum of photosynthetic reaction centers (Rb. sphaeroides wild type) is reported. This spectrum exhibits features which are not observed with excitation into either the Qx or Soret absorption bands. The spectral data indicate that the partial double-bond character is induced in the C9C10 bond of the isocyclic ring of one of the pigments via interactions with the protein. It is proposed that this modified pigment is the L-subunit bacteriopheophytin and that the preference for electron transfer to this molecule could be in part due to the change in electronic structure induced by the site-specific pigment-protein interaction.

Bacterial Proteins↗