Biomedical subjects

K Sauer

Publications and source records attributed to K Sauer.

At least 55 records · Page 3Linked to original sources

PubMed1995

The role of cyclin E in the regulation of entry into S phase.

Cyclin E is a crucial regulator of entry into S phase in higher eukaryotes and acts in association with the protein kinase cdk2. Cyclin E expression is transcriptionally controlled in mammalian cells resulting in a maximum just before entry into S phase. Premature expression of cyclin E advances entry into S phase, while lack of cyclin E prevents entry into S phase. Cyclin E/cdk2 activity is regulated at multiple levels (by transcription, phosphorylation and inhibitor proteins) and appears to be involved in triggering initiation of DNA replication and in regulating genes important for proliferation and progression through S phase.

CDC2-CDC28 Kinases↗

PubMed1994

Orientation of the oxygen-evolving manganese complex in a photosystem II membrane preparation: an X-ray absorption spectroscopy study.

X-ray absorption spectroscopy has been performed on oriented photosystem II membrane particles isolated from spinach. Structural features of the tetranuclear Mn cluster and the orientation of the cluster with respect to the lipid bilayer were determined in both the S1 and S2 states of the Kok cycle. Variation of the sample orientation with respect to the X-ray e-vector yields highly dichroic K-edge and extended X-ray absorption fine structure spectra (EXAFS), indicative of an asymmetric tetranuclear cluster. Mn-Mn vectors at 2.72 and 3.38 A can be resolved from these measurements using quantitative analysis. The 2.72-A vector, consisting of at least two component vectors, is oriented at an average angle of 60 degrees +/- 7 degrees to the membrane normal, with an average of 1.1 +/- 0.1 interactions per Mn atom. The 3.38-A vector, most probably an average of two vectors, makes an angle of 43 degrees +/- 10 degrees with respect to the membrane normal, with an average of 0.45 +/- 0.07 backscatterer per Mn atom. Upon advance to the S2 state, the orientation of these vectors and the average numbers of backscatterers are approximately invariant. Analysis of more subtle features of the EXAFS reveals changes accompanying this S-state advance that are consistent with the oxidation of Mn during this transition. However, the dominant structural features of the oxygen-evolving complex remain constant in the S1 and S2 states. The structure of the Mn complex and the orientation of the complex in the membrane within the context of dichroism of the X-ray absorption data are discussed.

Chloroplasts↗

PubMed1994

Spectroscopic studies of phycobilisome subcore preparations lacking key core chromophores: assignment of excited state energies to the Lcm, beta 18 and alpha AP-B chromophores.

Chromophore absorption and emission characteristics of the alpha AP-B, beta 18 and Lcm (large core-membrane linker) chromopeptides within the phycobilisome core are investigated using genetically engineered strains of Synechococcus sp. PCC 7002. Steady-state and time-resolved emission were used to examine energy transfer in subcore preparations from the wild-type organism and two mutants. Low-temperature (77 K) emission spectra were also measured for intact phycobilisomes from the wild-type and five mutant strains. Mutants retaining either the alpha AP-B subunit or the unaltered Lcm chromophore resulted in only small changes in the low-temperature emission spectra, while retention of only the beta 18 subunit resulted in blue-shifted emission spectra. The Lcm chromophore has a room-temperature absorption maximum at 675 nm. In phycobilisomes at 77 K the alpha AP-B and Lcm chromophores emit at 682-683 nm, and they are the best candidates for long-wavelength emitters also at room temperature. Overlap of these emission spectra with the absorption of chlorophyll a in the associated thylakoid membrane plays a significant role in excitation transfer from the antenna complexes in cyanobacteria.

Bacterial Proteins↗

PubMed1994

Correlation between structure and magnetic spin state of the manganese cluster in the oxygen-evolving complex of photosystem II in the S2 state: determination by X-ray absorption spectroscopy.

The structure of the manganese cluster in the S2 state with the g approximately 4 EPR signal (S2-g4 state) generated by 130 K illumination of photosystem II (PSII) membranes prepared from spinach has been investigated by X-ray absorption spectroscopy. The Mn X-ray absorption K-edge spectra of the S2-g4 state not only show a shift of the inflection point to higher energy from the S1 state but also reveal a different edge shape from that of the S2 state with the multiline signal (S2-MLS state). Extended X-ray absorption fine structure (EXAFS) studies of the Mn K-edge show that the structure of the Mn cluster in the S2-g4 state is distinctly different from those in the S2-MLS or S1 states. In the S2-g4 state, the second shell of back-scatters from the Mn absorber is found to contain two Mn-Mn distances of 2.73 and 2.85 A. We interpret this to indicate the presence of two nonequivalent di-mu-oxo-bridged Mn binuclear structures in the Mn cluster of the S2-g4 state. The third shell of the S2-g4 state at about 3.3 A also contains increased heterogeneity. By contrast, very little distance disorder was found to exist in the second shell of the S1 or S2-MLS states. A mechanism is proposed to explain these results in the context of our model for the Mn cluster and the EPR properties of the Mn complex in the S2 state.

Electron Spin Resonance Spectroscopy↗

PubMed1994

Cyclin E controls S phase progression and its down-regulation during Drosophila embryogenesis is required for the arrest of cell proliferation.

Most cells of the dorsal epidermis exit from the mitotic cycle after division 16 in Drosophila embryogenesis. This exit is dependent on the down-regulation of Drosophila cyclin E (DmcycE) during the final mitotic cycle. Ectopic expression of DmcycE after the final mitosis induces entry into S phase and reaccumulation of G2 cyclins and results in progression through a complete additional cell cycle. Conversely, analyses in DmcycE mutant embryos indicate that cyclin E is required for progression through S phase of the mitotic cycle. Moreover, endoreplication, which occurs in late wild-type embryos in the same pattern as DmcycE expression, is not observed in the mutant embryos. Therefore, Drosophila cyclin E, which forms a complex with the Dmcdc2c kinase, controls progression through S phase and its down-regulation limits embryonic proliferation.

Animals↗

PubMed1994

Catecholamine and blood lactate responses to incremental rowing and running exercise.

Ten collegiate rowers performed discontinuous incremental exercise to their tolerable limit on two occasions: once on a rowing ergometer and once on a treadmill. Ventilation and pulmonary gas exchange were monitored continuously, and blood was sampled from a venous catheter located in the back of the hand or forearm for determination of blood lactate ([La]) and plasma epinephrine ([Epi]) and norepinephrine ([NE]) concentrations. Thresholds for lactate (LT), epinephrine (Epi-T), and norepinephrine (NE-T) were determined for each subject under each condition and defined as breakpoints when plotted as a function of O2 uptake (VO2). For running, LT (3.76 +/- 0.18 l/min) was lower (P < 0.05) than Epi-T (4.35 +/- 0.14 l/min) and NE-T (4.04 +/- 0.19 l/min). For rowing, LT (3.35 +/- 0.16 l/min) was lower (P < 0.05) than Epi-T (3.72 +/- 0.22 l/min) and NE-T (3.70 +/- 0.18 l/min) and was lower (P < 0.05) than LT for running. Within each mode of exercise, Epi-T and NE-T did not differ. Because LT occurred at a significantly lower VO2 than either Epi-T or NE-T, we conclude that catecholamine thresholds, per se, were not the cause of LT. However, for both modes of exercise LT occurred at a plasma [Epi] of approximately 200-250 pg/ml (rowing, 221 +/- 48 pg/ml; running, 245 +/- 45 pg/ml); these concentrations are consistent with the plasma [Epi] reported necessary for eliciting increments in blood [La] during Epi infusion at rest. Plasma [NE] at LT differed significantly between modes (rowing, 820 +/- 127 pg/ml; running, 1,712 +/- 217 pg/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1993

Where plants make oxygen: a structural model for the photosynthetic oxygen-evolving manganese cluster.

In the photosynthetic evolution of oxygen, water oxidation occurs at a catalytic site that includes four manganese atoms together with the essential cofactors, the calcium and chlorine ions. A structural model and a determination of the manganese oxidation states based on x-ray absorption spectroscopy are presented. The salient features, in both higher plants and cyanobacteria, are a pair of di-mu-oxo bridged manganese binuclear clusters linked by a mono-mu-oxo bridge, one proximal calcium atom, and one halide. In dark-adapted samples, manganese occurs in oxidation states (III) and (IV). Data from oriented membranes display distinct dichroism, precluding highly symmetrical structures for the manganese complex.

Bridged-Ring Compounds↗

PubMed1992

The g = 2 multiline EPR signal of the S2 state of the photosynthetic oxygen-evolving complex originates from a ground spin state.

The amplitude of the g = 2 Mn 'multiline' EPR signal of the S2 state of the photosynthetic oxygen-evolving complex varies inversely with temperature, indicating that this signal arises from a ground spin state. Electron spin echo experiments at temperatures of 4.2 K and 1.4 K show such Curie-law behavior of the g = 2 multiline EPR signal, as do continuous-wave EPR experiments performed at a non-saturating microwave power in the range from 15.0 K to 4.2 K.

Electron Spin Resonance Spectroscopy↗

PubMed1992

Core mutations of Synechococcus sp. PCC 7002 phycobilisomes: a spectroscopic study.

Three cyanobacterial strains harboring mutations affecting phycobilisome (PBS) cores were studied using steady state absorption and fluorescence and time-resolved fluorescence. The apcF mutant, missing beta 18, and the apcDF mutant, missing both alpha APB and beta 18, showed only small spectroscopic differences from the wild-type strain; their PBS emission was blue shifted by 10 nm, whereas their absorption spectra and time-resolved fluorescence kinetics were virtually unchanged. The third mutant studied was the apcE/C186S mutant in which the chromophore-binding cysteine-186 in the LCM99 polypeptide has been substituted with serine. The apcE/C186S mutant contained a modified chromophore which significantly changed the spectroscopic properties of the PBS complex. The apcE/C186S PBS absorbed more than the wild-type strain at 705 nm, and the emission spectrum gave two peaks at 660 nm and 715 nm. The time-resolved kinetics of the apcE/C186S mutant PBS were also significantly altered from those of the wild-type strain.

Cyanobacteria↗

PubMed1992

The manganese site of the photosynthetic oxygen-evolving complex probed by EPR spectroscopy of oriented photosystem II membranes: the g = 4 and g = 2 multiline signals.

The g = 4 and g = 2 multiline EPR signals arising from the Mn cluster of the photosynthetic oxygen-evolving complex (OEC) in the S2 state were studied in preparations of oriented photosystem II (PSII) membranes. The ammonia-modified forms of these two signals were also examined. The g = 4 signal obtained in oriented PSII membranes treated with NH4Cl at pH 7.5 displays at least 16 partially resolved Mn hyperfine transitions with a regular spacing of 36 G [Kim, D.H., Britt, R.D., Klein, M.P., & Sauer, K. (1990) J. Am. Chem. Soc. 112, 9389-9391]. The observation of this g = 4 "multiline signal" provides strong spectral evidence for a tetranuclear Mn origin for the g = 4 signal and is strongly suggestive of a model in which different spin state configurations of a single exchange-coupled Mn cluster give rise to the g = 4 and g = 2 multiline signals. A simulation shows the observed spectrum to be consistent with an S = 3/2 or S = 5/2 state of a tetranuclear Mn complex. The resolution of hyperfine structure on the NH3-modified g = 4 signal is strongly dependent on sample orientation, with no resolved hyperfine structure when the membrane normal is oriented perpendicular to the applied magnetic field. The dramatic NH3-induced changes in the g = 4 signal resolved in the spectra of oriented samples are suggestive that NH3 binding at the Cl- site of the OEC may represent direct coordination of NH3 to the Mn cluster.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Membrane↗

PubMed1991

Isolation and characterisation of a bovine cDNA encoding eukaryotic initiation factor 2 alpha.

Two cDNA clones have been isolated, from a bovine lymphosarcoma library, that encode the alpha-subunit of eukaryotic initiation factor 2 (eIF-2 alpha). The predicted 315 amino acid sequence showed more than 99% amino acid identity with rat and human eIF-2 alpha. Galactose-regulated expression of a full length bovine eIF-2 alpha cDNA in yeast resulted in the synthesis of a polypeptide of the predicted molecular mass (36 kDa). Furthermore, the expressed polypeptide cross-reacted with an antibody raised against rabbit eIF-2 alpha confirming the identity of the cDNA.

Amino Acid Sequence↗

PubMed1991

Orientation and linear dichroism of Mastigocladus laminosus phycocyanin trimer and Nostoc sp. phycocyanin dodecamer in stretched poly(vinyl alcohol) films.

The linear dichroism (LD) spectra of the C-phycocyanin (C-PC) trimer disks oriented in poly(vinyl alcohol) films (PVA) at room temperature and at 95 K were determined. Utilizing the known atomic coordinates of the chromophores (Schirmer, T., Bode, W. and Huber, R. (1987) J. Mol. Biol. 196, 677-695) and theoretical estimates of the orientations of the transition dipole moments relative to the molecular framework, the LD spectra were simulated using the pairwise exciton interaction model of Sauer and Scheer (Biochim. Biophys. Acta 936 (1988) 157-170); in this model, the alpha 84 and beta 84 transition moments are coupled by an exciton mechanism, while the beta 155 chromophore remains uncoupled. Linear dichroism spectra calculated using this exciton model, as well as an uncoupled chromophore (molecular) model, were compared with experimental LD spectra. Satisfactory qualitative agreement can be obtained in both the exciton and molecular models using somewhat different relative values of the theoretically estimated magnitudes of the beta 155 oscillator strength. Because the relative contributions of each of the chromophores (and thus exciton components) to the overall absorption of the C-PC trimer are not known exactly, it is difficult to differentiate successfully between the molecular and exciton models at this time. The linear dichroism spectra of PC dodecamers derived from phycobilisomes of Nostoc sp. oriented in stretched PVA films closely resemble those of the C-PC trimers from Mastigocladus laminosus, suggesting that the phycocyanin chromophores are oriented in a similar manner in both cases, and that neither linker polypeptides nor the state of aggregation have a significant influence on these orientations and linear dichroism spectra. The LD spectra of oriented phycocyanins in stretched PVA films at low temperatures (95 K) appear to be of similar quality and magnitude as the LD spectra of single C-PC crystals (Schirmer, T. and Vincent, M.G. (1987) Biochim. Biophys. Acta 893, 379-385).

Color↗

PubMed1991

Electron spin echo envelope modulation spectroscopy supports the suggested coordination of two histidine ligands to the Rieske Fe-S centers of the cytochrome b6f complex of spinach and the cytochrome bc1 complexes of Rhodospirillum rubrum, Rhodobacter sphaeroides R-26, and bovine heart mitochondria.

Electron spin echo envelope modulation (ESEEM) experiments performed on the Rieske Fe-S clusters of the cytochrome b6f complex of spinach chloroplasts and of the cytochrome bc1 complexes of Rhodospirillum rubrum, Rhodobacter sphaeroides R-26, and bovine heart mitochondria show modulation components resulting from two distinct classes of 14N ligands. At the g = 1.92 region of the Rieske EPR spectrum of the cytochrome b6f complex, the measured hyperfine couplings for the two classes of coupled nitrogens are A1 = 4.6 MHz and A2 = 3.8 MHz. Similar couplings are observed for the Rieske centers in the three cytochrome bc1 complexes. These ESEEM results indicate a nitrogen coordination environment for these Rieske Fe-S centers that is similar to that of the Fe-S cluster of a bacterial dioxygenase enzyme with two coordinated histidine ligands [Gurbiel, R. J., Batie, C. J., Sivaraja, M., True, A. E., Fee, J. A., Hoffman, B. M., & Ballou, D. P. (1989) Biochemistry 28, 4861-4871]. The Rieske Fe-S cluster lacks modulation components from a weakly coupled peptide nitrogen observed in water-soluble spinach ferredoxin. Treatment with the quinone analogue inhibitor DBMIB causes a shift in the Rieske EPR spectrum to g = 1.95 with no alteration in the magnetic coupling to the two nitrogen atoms. However, the ESEEM pattern of the DBMIB-altered Rieske EPR signal shows evidence of an additional weakly coupled nitrogen similar to that observed in the spinach ferredoxin ESEEM patterns.

Animals↗

PubMed1991

Nitrogen ligation to manganese in the photosynthetic oxygen-evolving complex: continuous-wave and pulsed EPR studies of photosystem II particles containing 14N or 15N.

The possibility of nitrogen ligation to the Mn in the oxygen-evolving complex from photosystem II was investigated with electron paramagnetic resonance (EPR) and electron spin echo envelope modulation (ESEEM) spectroscopies using 14N- and 15N-labeled preparations. Oxygen-evolving preparations were isolated from a thermophilic cyanobacterium, Synechococcus sp., grown on a medium containing either 14NO3- or 15NO3- as the sole source of nitrogen. the substructure on the "multiline" EPR signal, which arises from Mn in the S2 state of the enzyme, was measured with continuous-wave EPR. No changes were detected in the substructure peak positions upon substitution of 15N for 14N, indicating that this substructure is not due to superhyperfine coupling from nitrogen ligands. To detect potential nitrogen ligands with superhyperfine couplings of lesser magnitude than could be observed with conventional EPR methods, electron spin-echo envelope modulation experiments were also performed on the multiline EPR signal. The Fourier transform of the light-minus-dark time domain ESEEM data shows a peak at 4.8 MHz in 14N samples which is absent upon substitution with 15N. This gives unambiguous evidence for weak hyperfine coupling of nitrogen to the Mn of the oxygen-evolving complex. Possible origins of this nitrogen interaction are discussed.

Cyanobacteria↗

PubMed1990

The S3 state of photosystem II: differences between the structure of the manganese complex in the S2 and S3 states determined by X-ray absorption spectroscopy.

O2-evolving photosystem II (PSII) membranes from spinach have been cryogenically stabilized in the S3 state of the oxygen-evolving complex. The cryogenic trapping of the S3 state was achieved using a double-turnover illumination of dark-adapted PSII preparations maintained at 240 K. A double turnover of PSII was accomplished using the high-potential acceptor, Q400, which is the high-spin iron of the iron-quinone acceptor complex. EPR spectroscopy was the principal tool establishing the S-state composition and defining the electron-transfer events associated with a double turnover of PSII. The inflection point energy of the Mn X-ray absorption K-edge of PSII preparations poised in the S3 state is the same as for those poised in the S2 state. This is surprising in light of the loss of the multiline EPR signal upon advancing to the S3 state. This indicates that the oxidative equivalent stored within the oxygen-evolving complex (OEC) during this transition resides on another intermediate donor which must be very close to the manganese complex. An analysis of the Mn extended X-ray absorption fine structure (EXAFS) of PSII preparations poised in the S2 and S3 states indicates that a small structural rearrangement occurs during this photoinduced transition. A detailed comparison of the Mn EXAFS of these two S states with the EXAFS of four multinuclear mu-oxo-bridged manganese compounds indicates that the photosynthetic manganese site most probably consists of a pair of binuclear di-mu-oxo-bridged manganese structures. However, we cannot rule out, on the basis of the EXAFS analysis alone, a complex containing a mononuclear center and a linear trinuclear complex. The subtle differences observed between the S states are best explained by an increase in the spread of Mn-Mn distances occurring during the S2----S3 state transition. This increased disorder in the manganese distances suggests the presence of two inequivalent di-mu-oxo-bridged binuclear structures in the S3 state.

Benzoquinones↗

PubMed1990

The S0 state of photosystem II induced by hydroxylamine: differences between the structure of the manganese complex in the S0 and S1 states determined by X-ray absorption spectroscopy.

Hydroxylamine at low concentrations causes a two-flash delay in the first maximum flash yield of oxygen evolved from spinach photosystem II (PSII) subchloroplast membranes that have been excited by a series of saturating flashes of light. Untreated PSII membrane preparations exhibit a multiline EPR signal assigned to a manganese cluster and associated with the S2 state when illuminated at 195 K, or at 273 K in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). We used the extent of suppression of the multiline EPR signal observed in samples illuminated at 195 K to determine the fraction of PSII reaction centers set back to a hydroxylamine-induced S0-like state, which we designate S0*. The manganese K-edge X-ray absorption edges for dark-adapted PSII preparations with or without hydroxylamine are virtually identical. This indicates that, despite its high binding affinity to the oxygen-evolving complex (OEC) in the dark, hydroxylamine does not reduce chemically the manganese cluster within the OEC in the dark. After a single turnover of PSII, a shift to lower energy is observed in the inflection of the Mn K-edge of the manganese cluster. We conclude that, in the presence of hydroxylamine, illumination causes a reduction of the OEC, resulting in a state resembling S0. This lower Mn K-edge energy of S0*, relative to the edge of S1, implies the storage and stabilization of an oxidative equivalent within the manganese cluster during the S0----S1 state transition. An analysis of the extended X-ray absorption fine structure (EXAFS) of the S0* state indicates that a significant structural rearrangement occurs between the S0* and S1 states. The X-ray absorption edge position and the structure of the manganese cluster in the S0* state are indicative of a heterogeneous mixture of formal valences of manganese including one Mn(II) which is not present in the S1 state.

Chlorophyll↗

PubMed1990

[Health hazards due to lead in an an accumulator-production plant of the Suhl district].

In a lead accumulator producing factory the health risk of workers has been studied for more than 30 years by means of measuring the lead concentration at the working places for many years and by carrying out several exposure tests on the 22 workmen. At most workshop places the maximum allowable concentration was considerably exceeded. In many workmen the concentration of lead in the blood and the delta aminolevulinic acid in the urine were increased above the control values. Since 1955 six occupational diseases have been diagnosed which demonstrates the high health risk.

Air Pollutants, Occupational↗

PubMed1989

Spectroscopic studies of cyanobacterial phycobilisomes lacking core polypeptides.

Synechococcus sp. PCC 7002 (Agmenellum quadruplicatum PR6) genes encoding two highly conserved phycobilisome core polypeptides, a small linker polypeptide (LC8, apcC) and the allophycocyanin-B alpha-subunit (alpha APB, apcD), respectively, were interrupted by insertion of restriction fragments carrying the neomycin phosphotransferase gene of Tn5. The interrupted genes were used to transform Synechococcus sp. PCC 7002 to kanamycin resistance. The apcC- mutant assembled phycobilisomes lacking the LC8 polypeptide and the apcD- mutant assembled phycobilisomes lacking alpha APB. No other differences between the compositions of the mutant and wild-type phycobilisomes were detected. The apcC- strain grew about 25% more slowly than the wild-type, and its phycobilisomes dissociated more rapidly in 0.33 M Na/K-PO4 (pH 8.0) or in 0.75 M Na/K-PO4 at pH 8.0, at 40 degrees C, than did those of the wild-type. The phycobilisomes of this mutant were indistinguishable from those of the wild-type with respect to absorption and circular dichroism spectra, as well as time-resolved fluorescence emission. Steady-state emission spectra indicate a small decrease in long wavelength (680 nm) emission from the apcC- phycobilisomes and a complementary increase in shorter wavelength (665 nm) emission, relative to wild-type phycobilisomes. Strain apcD- phycobilisomes appear to be functionally indistinguishable from those of the wild-type, in spite of the absence of the two alpha APB subunits which bear terminal acceptor bilins. The only spectroscopic difference was seen in the steady-state fluorescence emission, for which the emission of the mutant was about 15% higher than that of the wild-type and was slightly blue-shifted. A phenotype has yet to be found for the apcD- mutation.

Cloning, Molecular↗