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J R Norris

Publications and source records attributed to J R Norris.

At least 19 recordsLinked to original sources
PubMed1992

Femtosecond spontaneous-emission studies of reaction centers from photosynthetic bacteria.

Spontaneous emission from reaction centers of photosynthetic bacteria has been recorded with a time resolution of 50 fs. Excitation was made directly into both the special-pair band (850 nm) and the Qx band of bacteriochlorophylls (608 nm). Rhodobacter sphaeroides R26, Rhodobacter capsulatus wild type, and four mutants of Rb. capsulatus were studied. In all cases the fluorescence decay was not single exponential and was well fit as a sum of two exponential decay components. The short components are in excellent agreement with the single component detected by measurements of stimulated emission. The origin of the nonexponential decay is discussed in terms of heterogeneity, the kinetic scheme, and the possibility of slow vibrational relaxation.

Energy Transfer↗
PubMed1991

Mechanism of the initial charge separation in bacterial photosynthetic reaction centers.

The initial electron transfer in reaction centers from Rhodobacter sphaeroides R26 was studied by a subpicosecond transient pump-probe technique. The measured kinetics at various wavelengths were analyzed and compared with several mechanisms for electron transfer. An unambiguous determination of the initial electron transfer mechanism in reaction centers cannot be made by studying the anion absorption region (640-690 nm), due to the spectral congestion in this region. However, correlations between the stimulated emission decay of the excited state of the special pair, P*, at 926 nm and bleaching of the bacteriopheophytin Qx absorption at 545 nm suggest that the electron transfer at 283 K is dominated by a two-step sequential mechanism, whereas one-step superexchange and the two-step sequential mechanism have about equal contributions at 22 K.

Electron Transport↗
PubMed1990

Contribution of vitamin K1 to the electron spin polarization in spinach photosystem I.

The electron spin polarized (ESP) electron paramagnetic resonance (EPR) signal observed in spinach photosystem I (PSI) particles was examined in preparations depleted of vitamin K1 by solvent extraction and following biological reconstitution by the quinone. The ESP EPR signal was not detected in the solvent-extracted PSI sample but was restored upon reconstitution with either protonated or deuterated vitamin K1 under conditions that also restored electron transfer to the terminal PSI acceptors. Reconstitution using deuterated vitamin K1 resulted in a line narrowing of the ESP EPR signal, supporting the conclusion that the ESP EPR signals in the reconstituted samples arise from a radical pair consisting of the oxidized PSI primary donor, P700+, and reduced vitamin K1.

Electron Spin Resonance Spectroscopy↗
PubMed1990

EPR characterization of genetically modified reaction centers of Rhodobacter capsulatus.

Electron paramagnetic resonance (EPR) has been used to investigate the cation and triplet states of Rhodobacter capsulatus reaction centers (RCs) containing amino acid substitutions affecting the primary donor, monomeric bacteriochlorophylls (Bchls), and the photoactive bacteriopheophytin (Bphe). The broadened line width of the cation radical in HisM200----Leu and HisM200----Phe reaction centers, whose primary donor consists of a Bchl-Bphe heterodimer, indicates a highly asymmetric distribution of the unpaired electron over the heterodimer. A T0 polarized triplet state with reduced yield is observed in heterodimer-containing RCs. The zero field splitting parameters indicate that this triplet essentially resides on the Bchl half of the heterodimer. The cation and triplet states of reaction centers containing HisM200----Gln, HisL173----Gln, GluL104----Gln, or GluL104----Leu substitutions are similar to those observed in wild type. Oligonucleotide-mediated mutagenesis has been used to change the histidine residues that are positioned near the central Mg2+ ions of the reaction center monomeric bacteriochlorophylls. Reaction centers containing serine substitutions at M180 and L153 or a threonine substitution at L153 have unaltered pigment compositions and are photochemically active. The cation and triplet states of HisL153----Leu reaction centers are similar to those observed in wild type. Triplet energy transfer to carotenoid is not observed at 100 K in HisM180----Arg chromatophores. These results have important implications for the structural requirements of tetrapyrrole binding and for our understanding of the mechanisms of primary electron transfer in the reaction center.

Bacteriochlorophylls↗
PubMed1990

Stark effect in wild-type and heterodimer-containing reaction centers from Rhodobacter capsulatus.

The effect of an external electric field on the optical absorption spectra of wild-type Rhodobacter capsulatus and two Rb. capsulatus reaction centers that have been genetically modified through site-directed mutagenesis (HisM200----LeuM200 and HisM200----PheM200) was measured at 77 K. The two genetically modified reaction centers replace histidine M200, the axial ligand to the M-side bacteriochlorophyll of the special pair, with either leucine or phenylalanine. These substitutions result in the replacement of the M-side bacteriochlorophyll with bacteriopheophytin, forming a bacteriochlorophyll-bacteriopheophytin heterodimer. The magnitude of the change in dipole moment from the ground to excited state (delta mu app) and the angle delta between the Qy transition moment and the direction of delta mu app were measured for the special pair absorption band for all three reaction centers. The values for delta mu app and delta obtained for wild-type Rb. capsulatus (delta mu app = 6.7 +/- 1.0 D, delta = 38 +/- 3 degrees) were the same within experimental error as those of Rhodobacter sphaeroides and Rhodopseudomonas viridis. The values for delta mu app and delta obtained for the red-most Stark band of both heterodimers were the same, but delta mu was substantially different from that of wild-type reaction centers (HisM200----LeuM200, delta mu app greater than or equal to 14.1 D and delta = 33 +/- 3 degrees; HisM200----PheM200, delta mu app greater than or equal to 15.7 D and delta = 31 +/- 4 degrees).(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial Proteins↗
PubMed1990

Tyrosine- and phenylalanine-restricted formula diet augments immunocompetence in healthy humans.

Previous studies indicate that limiting tyrosine and phenylalanine intake in the diet decreases tumor growth and metastasis. General health status, immune status, and platelet function were studied in nine healthy human subjects consuming low-protein foods supplemented with formula diets free of tyrosine and phenylalanine to maintain total daily intake of tyrosine at 2.4 mg/kg body wt and phenylalanine at 3.5 mg/kg body wt. This regimen decreased plasma tyrosine (p less than 0.05) but not phenylalanine. Blood indicators of protein status were not changed. Platelet aggregation decreased in response to adenosine diphosphate and platelet activating factor in seven of nine subjects. Natural killer, T-helper, and T-cytotoxic/suppressor lymphocyte numbers proportionally increased relative to neutrophils (p less than 0.05). Natural killer cell activity increased in six of nine subjects. Increased natural killer cell activity and decreased platelet aggregation are two indices associated with decreased tumor growth and metastasis.

Body Composition↗
PubMed1989

Correlation of paramagnetic states and molecular structure in bacterial photosynthetic reaction centers: the symmetry of the primary electron donor in Rhodopseudomonas viridis and Rhodobacter sphaeroides R-26.

The orientation of the principal axes of the primary electron donor triplet state measured in single crystals of photosynthetic reaction centers is compared to the x-ray structures of the bacteria Rhodobacter (Rb.) sphaeroides R-26 and Rhodopseudomonas (Rps.) viridis. The primary donor of Rps. viridis is significantly different from that of Rb. sphaeroides. The measured directions of the axes indicate that triplet excitation is almost completely localized on the L-subunit half of the dimer in Rps. viridis but is more symmetrically distributed (approximately 63% on the L half of the special pair and approximately 37% on the M half) on the dimeric donor in Rb. sphaeroides R-26. The large reduction of the zero field splitting parameters relative to monomeric bacteriochlorophyll triplet in vitro suggests significant participation of asymmetrical charge transfer electronic configurations in the special pair triplet state of both organisms (approximately 23% in Rps. viridis and approximately 13% in Rb. sphaeroides).

Bacterial Proteins↗
PubMed1988

An assessment of taxonomic congruence between DNA-DNA hybridization and pyrolysis gas-liquid chromatographic classifications.

The existence of subgroups within Bacillus megaterium has been reported previously on the basis of DNA-DNA hybridization and DNA base composition studies. In this study the strains used to define these subgroups have been reanalysed by pyrolysis gas-liquid chromatography. The resultant two-group classification of the test strains was directly comparable with that obtained from the previous nucleic acid analyses at the between-group level. However, comparisons of the test strains at the within-group level proved less successful.

Bacillus megaterium↗
PubMed1988

Reproducibility of pyrolysis mass spectrometry: effect of growth medium and instrument stability on the differentiation of selected Bacillus species.

The discrimination of a set of 53 strains, taken from four closely related Bacillus species (Bacillus subtilis, B. pumilus, B. licheniformis and B. amyloliquefaciens), was examined using pyrolysis mass spectrometry. Strains were grown on six different media to examine the effect of media variation, especially batch-to-batch variation of a single medium, on the pyrolysis mass spectra and strain discrimination achieved. Long-term reproducibility over a period of 14 months was also examined. It was shown that batch-to-batch media variation is insufficient to affect spectra and strain discrimination significantly, but different media types do affect this. It was shown that species groups could still be recovered from the data, however, with an appropriate data-handling system. It was not possible to directly compare spectra produced 14 months apart, but the strain and species discrimination achieved using each data-set were highly comparable.

Bacillus↗
PubMed1985

Subclassification of neurons in the ventrobasal complex of the dog: quantitative Golgi study using principal components analysis.

The neuronal architecture of the ventrobasal complex (VB) in dog is examined in coronal and horizontal brain sections processed by Golgi- and Nissl-staining methods. Presumed projection and intrinsic neurons are identified by differences in soma size and shape, dendritic branch pattern, the morphology and distribution of appendages, and the appearance of axons. Forty-five projection neurons are examined by quantifying (1) soma cross-sectional area, (2) dendritic field extent and shape, (3) appendages on the soma, primary dendrites, and in a defined major dendritic branch zone, and (4) location in the VB. When considered independently, each variable offers little evidence for separation into morphological classes. However, several of the variables have wide ranges and show significant correlation with other parameters. Using the multivariate descriptive methods of principal components analysis and cluster analysis, a separation of the projection neurons into three morphological classes designated as large, medium, and small neurons is indicated. The features most critical in distinguishing between the groups are, in descending order of importance: (1) dendritic field extent; (2) number of primary dendrites; (3) soma cross-sectional area; (4) number of appendages per major branch point (MBP); (5) number of appendages on the soma; and, (6) number of appendages on the primary dendrites. Dendritic field shape and neuron location have little influence in determining classification.

Analysis of Variance↗
PubMed1985

Subclassification of neurons in the subthalamic nucleus of the lesser bushbaby (Galago senegalensis): a quantitative Golgi study using principal components analysis.

The morphology of neurons in the subthalamic nucleus (STN) of the lesser bushbaby (Galago senegalensis) is described in coronal brain sections processed by Golgi- and Nissl-staining techniques. Quantitative and statistical methods are used to evaluate (1) soma size and shape, (2) dendritic field size, shape, and branch frequency, (3) the number of dendritic and somatic spines per neuron, and (4) neuron location within the STN. Principal components analysis of these variables suggests that three classes of neurons are present. Two of these classes are considered to be projection cells, referred to as elongate-fusiform and radiate neurons, respectively. Elongatefusiform neurons have somata and dendritic fields which are large in diameter, extremely fusiform in shape, and give rise to few appendages. Somata and dendritic fields of radiate neurons are smaller in diameter, more rounded in shape, and support more spines than the elongate-fusiform neurons. The third class of cells in Galago STN is tentatively identified as consisting of interneurons on the basis of small soma and dendritic field size, thin and varicose dendritic morphology, and the presence of multilobulated dendritic appendages.

Animals↗
PubMed1984

The cytoarchitecture and some efferent projections of the centromedian-parafascicular complex in the lesser bushbaby (Galago senegalensis).

The morphology of neurons in the centromedian (CM) and parafascicular (PF) nuclei in the lesser bushbaby (Galago senegalensis) is described in coronal and horizontal brain sections using Golgi-, horseradish peroxidase (HRP)-, and Nissl-staining procedures. The CM contains two types of cells referred to as principal neurons and Golgi type II (like) neurons. Cell bodies of principal neurons are relatively large in cross-sectional area (mean = 130.42 micron2), round to spindle in shape, support short somatic spines, and give rise to three to five primary dendrites. The dendrites branch in a "radiate" pattern and possess numerous appendages consisting of narrow, stalk-supported swellings. The presumed axons of these cells are impregnated only in their initial segments. On the basis of the similarity of principal neuron soma shapes and cross-sectional areas with those of HRP-reactive somata following cortical HRP implantation, it is concluded that at least some of the principal neurons in Galago CM project to somatic sensory-motor cortex. Golgi type II (like) neurons have small (mean = 79.43 micron2), round somata which support several spines and give rise to three to four small-diameter dendrites. The dendrites are infrequently branched, sinuous in their courses, and give rise to complex appendages and beaded processes. However, the axons of these cells could not be seen to ramify in the immediate vicinity of the dendritic field or soma, and there is considerable overlap in the cross-sectional areas of Golgi type II (like) neurons seen in Golgi preparations and HRP-stained cells following cortical implant of HRP pellets. Consequently, although Golgi type II (like) cells have traits characteristic of classically described intrinsic neurons, a cortical projection of these cells cannot be ruled out by the present study. The parafascicular nucleus contains two groups of large, radiate cells characterized by the presence or absence of somatic spines. Cells with somatic spines also contain numerous appendages on the dendrites. Cells without somatic spines support only a few, isolated, short dendritic appendages. Numerous small cell-bodied neurons are present in Nissl-stained sections of PF; however, cells which resemble Golgi type II neurons were not observed in the PF in the present Golgi-impregnated material. In contrast to the CM, the large cell-bodied neurons in PF were not found to project to somatic sensory-motor cortex in Galago.

Animals↗
PubMed1984

Curie-point pyrolysis mass spectrometry applied to characterization and identification of selected Bacillus species.

The use of pyrolysis mass spectrometry in the characterization and identification of Bacillus species was studied. Fifty-three strains of four closely related groups, Bacillus subtilis, B. pumilus, B. licheniformis and 'B. amyloliquefaciens', were used in a study of both sporulated and nonsporulated cultures. Pyrolysis was carried out using a Pyromass 8-80, a novel pyrolysis mass spectrometer specifically designed for fingerprinting complex samples. The pyrolysis data obtained were analysed using multivariate statistical techniques. All four groups could be differentiated using data from non-sporulated cultures but the data from sporulated cultures did not separate B. subtilis from 'B. amyloliquefaciens' or B. pumilus. In contrast, B. licheniformis was more clearly differentiated from the other three species using these data. Culture maturity affected the mass spectra obtained from non-sporulated cultures.

Bacillus↗
PubMed1983

A Golgi study of the opossum ventral basal complex.

The morphology of neurons in the ventral basal complex (VBC) of the adult opossum (Didelphis virginiana) is described from thick coronal brain sections, using Golgi-, horseradish peroxidase (HRP)-, and Nissl-staining methods. Soma cross-sectional area, dendritic field shape, and the number of appendages (spines) in a defined major branch zone (MBZ) are quantified and statistically analyzed. Results indicate that neurons in opossum VBC have relatively large cell bodies, dendrites which branch in a tufted pattern, and numerous dendritic appendages. These neurons are designated as relay cells because of (1) their tufted dendritic branch patterns, considered characteristic of thalamic relay cells (Ramon-Moliner, '62), and (2) the similarity of their soma sizes with HRP-labeled somata after somatosensory cortical injections. Neurons with traditionally described interneuron morphology do not appear to be present in the VBC of this animal, and, in this respect, the neuronal morphology of opossum VBC is similar to that in rat (McAllister and Wells, '81). Based on statistical analysis of the structural features observed, the presumed relay cells in opossum VBC do not show significant differences in morphology, and consequently are not subdivided into classes. Opossum VBC neurons are recognized as forming a single category in which broad and continuous variations in morphology are indicated. Recognition of a singular class of relay cell is consistent with descriptions for rat and cat VBC (Scheibel and Scheibel, '66), but at variance with a previous report for the primate Galago VBC (Pearson and Haines, '80) subdividing thalamic relay cells into Types I, II, and intermediate categories.

Animals↗
PubMed1982

Factors influencing intake of high urea-containing rations by lactating dairy cows.

In a series of experiments we investigated effects of several factors on intake of urea by lactating dairy cows. Cows given an unfamiliar ingredient or altered moisture in the ration reduced their intake, and this effect was attributed to a newness factor. Addition of urea to a ration may have a similar effect. An experimental design providing both no-choice and two-choice data was devised to minimize the effect of newness. When urea was isolated physically by pellets coated with ground corn, cows selected against urea-containing pellets on a two-choice basis and reduced intake on a no-choice basis. When the choice was between two urea-containing rations, cows preferred the pellets in which urea flavor and odor should have been most evident. Urea odor in the feedbox or urea in the drinking water did not reduce feed intake. Eating rate of a 2.5% urea-containing ration over two daily 30-min feeding periods was about one-half that of a non-urea ration. This effect was evident during the first 5-min eating interval. Administration of urea solution into the rumen prior to feeding a nonurea ration markedly reduced subsequent intake. Reticulum pH and ammonia indicated possible sublethal ammonia toxicity. Intake and eating rate were depressed and reticulum pH was elevated when cows were fed a ration with 2.5% urea versus 1% urea or nonurea rations. Elevated reticulum ammonia occurred on both 1 and 2.5% urea-containing rations. Cows not previously exposed to urea-containing rations reduced intake and eating rate when fed rations with 2.0 and 2.5% urea. Intake reduction was not comparable to that by cows preconditioned to urea rations. Upon third exposure to 2.5% urea in the ration, cows reduced and ceased intake but readily consumed a nonurea ration. Cows require preconditioning to develop a negative aversion to rations containing high urea, perhaps through a mechanism of sublethal ammonia toxicity.

Ammonia↗
PubMed1980

Discrimination of micro-organisms using direct probe mass spectrometry.

Direct probe mass spectrometry of single colonies of different bacteria produced spectra which could be distinguished by calculations based on the intensities of 25 selected ions. Direct probe mass spectrometry has enormous potential as a rapid technique for characterizing micro-organisms.

Ions↗