Effects of relative band intensity on prediction of protein secondary structure from CD

Increasing the magnitude of a protein CD spectrum obviously increases the magnitude of each predicted secondary structure by the same amount. However, increasing the magnitude of the negative, long-wave-length portion of a protein CD spectrum usually has the opposite effect from increasing the positive, short-wave-length portion. Thus small distortions in the CD spectra of proteins at short wavelength can have a significant effect on the analysis for secondary structure. This measurement error and its effect on the analysis are systematically investigated for 16 proteins of known structure. The results demonstrate that a two-point calibration of a CD instrument is mandatory to avoid serious errors when estimating secondary structure from protein CD spectra.     

Temporal dynamics of chromatic tuning in macaque primary visual cortex

The ability to distinguish colour from intensity variations is a difficult computational problem for the visual system because each of the three cone photoreceptor types absorb all wavelengths of light, although their peak sensitivities are at relatively short (S cones), medium (M cones), or long (L cones) wavelengths. The first stage in colour processing is the comparison of the outputs of different cone types by spectrally opponent neurons in the retina and upstream in the lateral geniculate nucleus. Some neurons receive opponent inputs from L and M cones, whereas others receive input from S cones opposed by combined signals from L and M cones. Here we report how the outputs of the L/M- and S-opponent geniculate cell types are combined in time at the next stage of colour processing, in the macaque primary visual cortex (V1). Some V1 neurons respond to a single chromatic region, with either a short (68-95 ms) or a longer (96-135 ms) latency, whereas others respond to two chromatic regions with a difference in latency of 20-30 ms. Across all types, short latency responses are mostly evoked by L/M-opponent inputs whereas longer latency responses are evoked mostly by S-opponent inputs. Furthermore, neurons with late S-cone inputs exhibit dynamic changes in the sharpness of their chromatic tuning over time. We propose that the sparse, S-opponent signal in the lateral geniculate nucleus is amplified in area V1, possibly through recurrent excitatory networks. This results in a delayed, sluggish cortical S-cone signal which is then integrated with L/M-opponent signals to rotate the lateral geniculate nucleus chromatic axes.     

Structural studies of the melibiose permease of Escherichia coli by fluorescence resonance energy transfer. I. Evidence for ion-induced conformational change

Further insight into the cosubstrate-induced structural change of the melibiose permease (MelB) of Escherichia coli has been sought by investigating the binding and spectroscopic properties of the fluorescent sugar 2'-(N-5-dimethylaminonaphthalene-1-sulfonyl)aminoethyl 1-thio-beta-D-galactopyranoside (Dns2-S-Gal) and related analogs (Dns3-S-Gal or Dns6-S-Gal with a propyl or hexyl instead of an ethyl linker, respectively) interacting with MelB in membrane vesicles or in proteoliposomes. The three analogs efficiently inhibit melibiose transport and bind to MelB in a sodium-dependent fashion. Their dissociation constants (Kd) are in the micromolar range in the presence of NaCl and an order of magnitude higher in its absence. In the presence of NaCl and Dns2-S-Gal, sample excitation at 335 or 297 nm gives rise to a fluorescent signal at around 465 nm, whereas Dns3-S-Gal or Dns6-S-Gal emits a fluorescence light at 490 or 506 nm, respectively. Detailed study of the Dns2-S-Gal signal elicited by a 297 nm illumination indicates that a tryptophan-mediated fluorescence resonance energy transfer phenomenon is involved in the response. All fluorescence signals below 500 nm are prevented by addition of melibiose in excess, and the kinetic constants describing their dependence on the probe or NaCl concentrations closely correlate with the probe binding constants. Finally, the Dns2-S-Gal signal recorded in sodium-free medium is red shifted by up to 25 nm from that recorded in the presence of NaCl. Taken together, these results suggest (i) that the fluorescence signals below 500 nm arise from Dns-S-Gal molecules bound to MelB, (ii) the presence of a highly hydrophobic environment close to or at the sugar-binding site, the polarity of which increases on moving away from the sugar-binding site, and (iii) that the interaction of sodium ions with MelB enhances the hydrophobicity of this environment. These results are consistent with the induction of a cooperative change of the structure of the sugar-binding site or of its immediate vicinity by the ions.     

Contrast enhancement and distributed encoding by bipolar cells in the retina

Responses of bipolar cells, cone photoreceptors, and horizontal cells were recorded intracellularly in superfused eyecup preparations of the tiger salamander (Ambystoma tigrinum). Contrast flashes of positive and negative polarity were applied at the center of the receptive field while the entire retina was light adapted to a background field of 20 cd/m2. For small contrasts, many bipolar cells showed remarkably high contrast gain: up to 15-20% of the bipolar response was evoked by a contrast step of 1%. There was considerable variation from cell to cell but, on average, no striking differences in contrast gain were found between the depolarizing (Bd) and hyperpolarizing (Bh) bipolar cells. Quantitative comparisons of contrast/response measurements for cone photoreceptors and cone-driven bipolars suggest that the high contrast gain of bipolars is the consequence of a 5-10 x amplification of small signals across the cone-->bipolar synapse. Bipolar cells had a very restricted linear range of response and tended to saturate at stimulus levels that were within the linear range of the cone response. The contrast/response of horizontal cells was similar to that of cones and differed markedly from that of Bh cells. For steps of equal contrast, the latency of the Bh cells was approximately 20 ms shorter than that of the Bd cells regardless of the contrast magnitude. For both bipolar cells and cones, the effect of contrast polarity on latency seems largely due to the absolute value of the light step, delta L. In the large signal domain, properties of the contrast responses of bipolar cells varied appreciably, both within and between the Bd and Bh classes. Cells of either class could be positive- or negative-contrast dominant. These and additional results show that in the light-adapted retina, the bipolar population is functionally diverse and has the potential to provide a rich substrate for distributed encoding of visual images.     

Masking with interaurally delayed stimuli: the use of "internal" delays in binaural detection

Detectability of 500-Hz tones was measured in the presence of broadband masking noise using three types of binaural conditions. In the first, the masker was presented diotically and the tone was interaurally delayed. In the second, the masker was interaurally delayed and the 500-Hz tone was presented either in phase (S0) or out of phase (S pi). In the third, the masker consisted of the sum of two independent noises having interaural delays of equal magnitude and opposite sign. The signal was, once more, presented either in phase (S0) or out of phase (S pi). Comparisons among the data and quantitative analyses assuming the use of compensatory "internal delays" suggested that internal delays are operative and compensate accurately for external delays of up to approximately 750 microseconds. The analyses also indicated that larger internal delays (i.e., up to 2 to 3 ms) are probably also operative. However, performance using such large internal delays appears to be degraded in accord with the hypothesis that their application introduces "noise" in the internal representation of the stimuli.     

A Study of the Higher Electronic Transitions of Selenoformaldehyde, CH2Se

The pi --> pi* and n --> 5s absorption spectra of selenoformaldehyde, CH2Se and CD2Se, are reported. Both spectra are diffuse. The pi --> pi* transition extends from 243 to 210 nm with an extensive Franck-Condon profile and intensity maximum estimated at 230 nm. The Rydberg n --> 5s transition is superimposed on the pi --> pi* system. While still diffuse, the system is less extensive and shows an intensity maximum at 235 nm. The corresponding Rydberg transition of the deuterated species is blue shifted by 140 cm-1. Copyright 1999 Academic Press.     

Beta-endorphin response to exercise. An update

Opioid receptor subtype antagonists differentially alter food intake under deprivation (24 h), glucoprivic (2-deoxy-D-glucose, 500 mg/kg, i.p.) or palatable (10% sucrose) conditions with mu (beta-funaltrexamine) and kappa (nor-binaltorphamine), but not delta1 ([D-Ala2,Leu5,Cys6]enkephalin) opioid antagonists reducing each form of intake following ventricular microinjection. Both mu and kappa opioid antagonists microinjected into either the hypothalamic paraventricular nucleus or the nucleus accumbens reduce intake under deprivation and glucoprivic conditions. Palatable intake is reduced by both antagonists in the paraventricular nucleus, but only mu antagonists are active in the accumbens. Food intake is stimulated by mu and delta, but not kappa, opioid agonists microinjected into the ventral tegmental area. The present study examined whether food intake under either deprivation, glucoprivic or palatable conditions was altered by bilateral administration of general (naltrexone), mu, kappa, delta1 or delta2 (naltrindole isothiocyanate) opioid antagonists into the ventral tegmental area. Deprivation (24 h)-induced feeding was significantly reduced by high (50 microg), but not lower (10-20 microg) doses of naltrexone (21%), and by delta2 (4 microg, 19%) antagonism in the ventral tegmental area. 2-Deoxy-D-glucose (500 mg/kg, i.p.)-induced hyperphagia was significantly reduced by high (50 microg), but not lower (20 microg) doses of naltrexone (64%), and by delta2 (4 microg, 27%) antagonism in the ventral tegmental area. Sucrose (10%) intake was significantly reduced by naltrexone (20-50 microg, 25-39%) and delta2 (4 microg, 25%) antagonism in the ventral tegmental area. Neither mu, kappa nor delta1 antagonists were effective in reducing any form of intake following microinjection into the ventral tegmental area. These data indicate that the ventral tegmental area plays a relatively minor role in the elicitation of these forms of food intake, and that delta2, rather than mu, kappa or delta1 opioid receptors appear responsible for mediation of these forms of intake by this nucleus.     

Responses of neurons in the inferior colliculus to binaural masking level difference stimuli measured by rate-versus-level functions

The psychophysical detection threshold of a low-frequency tone masked by broadband noise is reduced by < or = 15 dB by inversion of the tone in one ear (called the binaural masking level difference: BMLD). The contribution of 120 low-frequency neurons (best frequencies 168-2,090 Hz) in the inferior colliculus (ICC) of the guinea pig to binaural unmasking of 500-Hz tones masked by broadband noise was examined. We measured rate-level functions of the responses to identical signals (So) and noise (No) at the two ears (NoSo) and to identical noise but with the signal inverted at one ear (NoS pi): the noise was 7-15 dB suprathreshold. The masked threshold was estimated by the standard separation, "D". The neural BMLD was estimated as the difference between the masked thresholds for NoSo and NoS pi. The presence of So and S pi tones was indicated by discharge rate increases in 55.3% of neurons. In 36.4% of neurons, the presence of So tones was indicated by an increase in discharge rate and S pi tones by a decrease. In 6.8% of neurons, both So and S pi tones caused a decrease in discharge rate. In only 1.5% of neurons was So indicated by a decrease and S pi by an increase in discharge rate. Responses to the binaural configurations were consistent with the neuron's interaural delay sensitivities; 34.4% of neurons showing increases in discharge rate to both So and S pi tones gave positive BMLDs > or = 3 dB (S pi tones were detected at lower levels than So), whereas 37.3% gave negative BMLDs > or = 3 dB. For neurons in which So signals caused an increase in the discharge rate and S pi a decrease, 72.7% gave positive BMLDs > or = 3 dB and only 4.5% gave negative BMLDs > or = 3 dB. The results suggest that the responses of single ICC neurons are consistent with the psychophysical BMLDs for NoSo versus NoS pi at 500 Hz, and with current binaural interaction models based on coincidence detection. The neurons likely to contribute to the psychophysical BMLD are those with BFs near 500 Hz, but detection of So and S pi tones may depend on different populations of neurons.     

Isoform-specific biotransformation of glyceryl trinitrate by rat aortic glutathione S-transferases

The objective of this study was to purify and characterize rat aortic glutathione S-transferases (GSTs) and to assess their role in the biotransformation of the nitrovasodilator, glyceryl trinitrate (GTN). Two class alpha GSTs (Ya and Yc) a class mu GST (Yb2) and a class pi GST (Yp) were identified in rat aortic cytosol. Partial purification of three of these (Yb2, Yc and Yp) was achieved by affinity chromatography with S-hexylglutathione agarose. Further purification by cation- and anion-exchange chromatography resulted in the purification of GST Yc and GST Yb2/Yp to apparent homogeneity, a purification of 200- and 110-fold, respectively. Purified GST Yc and Yb2/Yp mediated GTN biotransformation with similar rates. GST activity and GTN biotransformation by rat aortic cytosol and affinity-purified GSTs were highly sensitive to inhibition by the class mu selective inhibitors Basilen Blue and bromosulfophthalein. Removal of GST Yb2 from rat aortic cytosol by immunoprecipitation resulted in marked inhibition of GST activity and GTN biotransformation. We conclude that the GSTs account for the major portion of GTN biotransformation in rat aortic cytosol, and that this is primarily attributable to the GST Yb2 isoform.     

The cone/horizontal cell network: a possible site for color constancy

Color vision is spectrally opponent, suggesting that spectrally opponent neurons, such as the horizontal cells in fish and turtle retinae, play a prominent role in color discrimination. In the accompanying paper (Kraaij et al., 1998), it was shown that the output signal of the horizontal cell system to the cones is not at all spectrally opponent. Therefore, a role for the spectrally opponent horizontal cells in color discrimination seems unlikely. In this paper, we propose that the horizontal cells play a prominent role in color constancy and simultaneous color contrast instead of in color discrimination. We have formulated a model of the cone/horizontal cell network based on measurements of the action spectra of the cones and of the feedback signal of the horizontal cell system to the various cone types. The key feature of the model is (1) that feedback is spectrally and spatially very broad and (2) that the gain of the cone synapse strongly depends on the feedback strength. This makes the synaptic gain of the cones strongly dependent on the spectral composition of the surround. Our model, which incorporates many physiological details of the outer retina, displays a behavior that can be interpreted as color constancy and simultaneous color contrast. We propose that the horizontal cell network modulates the cone synaptic gains such that the ratios of the cone outputs become almost invariant with the spectral composition of the global illumination. Therefore, color constancy appears to be coded in the retina.     

Oxidation of porous nanocrystalline titanium nitride. I. Kinetics

We used the continuous weighing method to study the oxidation kinetics in air for TiN specimens pressed and sintered from nanocrystalline powders with particle size ≤55 nm. Oxidation was carried out at 500–1000 °C for 240 min. By comparing with the oxidizability of compact titanium, we estimated the total reaction surface S of the porous specimens as a function of their oxidation conditions. The mass of absorbed oxygen Δm was calculated from the mass gain ΔP, taking into account the volatile component N₂. We have shown that the maximum mass gain Δm at 600 °C is due to reaction of oxygen with the largest reaction surface. Within 120 min, external pores close up, S decreases, and then a continuous oxide layer forms in which diffusion of oxygen is slowed down. At 700–800 °C, the process of closing up of the pores is activated, and S decreases by an order of magnitude compared to 600 °C. After the first 40–50 min, a continuous oxide film forms and virtually no further mass gain occurs. As the temperature increases, the oxidation rate increases. At 900 °C, the reaction surface becomes equal to the external surface of the specimen, but the thickness of the scale increases linearly. We hypothesize that for T > 850 °C, counterdiffusion of titanium ions is superimposed on diffusion of oxygen. __________ Translated from Poroshkovaya Metallurgiya, Nos. 1–2(447), pp. 98–103, January–February, 2006.     

双波长分光光度法同时测定含铑、金、硒、碲冶金物料中铂、钯的研究

针对铑、金、硒、碲严重干扰用二苄基二硫化乙二酰胺(DbDO)为显色剂测定铂的问题,研究用碘化钾和抗坏血酸作还原剂,以双波长分光光度法同时测定铂、钯.在2～3mol/L HCl中,铂、钯—DbDO配合物经萃取显色,三氯甲烷萃取液经>8mol/L HCl洗涤后,配合物颜色稳定,吸光度恒定可获得最大值.钯用双波长等吸收波长法(λ_2=454nm,λ_1=548.5nm),铂用双波长倍率系数法(λ_2’=521nm,λ_1’=500nm,K=2.521).     

Are some of the effects of ethanol mediated through NPY?

One proposed mechanism for underpinning colour constancy is computation of the relative activity of cones within one class--cone ratios, or cone contrasts--between surfaces in a fixed scene undergoing a change in illuminant. Although there is evidence that cone ratios do determine colour appearance under many conditions, the site or sites of their computation is unknown. Here, we report that a cerebrally achromatopsic observer, MS, displayed evidence of colour constancy in asymmetric colour matching tasks and was able to discriminate changes in cone ratios for simple, but not complex scenes. We hypothesise that the site of local cone-ratio computation is therefore early in the visual system, probably retinal.     

UV- and midwave-sensitive cone-driven retinal responses of the mouse: a possible phenotype for coexpression of cone photopigments

Molecular biological, histological and flicker electroretinographic results have established that mice have two cone photopigments, one peaking near 350 nm (UV-cone pigment) and a second near 510 nm [midwave (M)-cone pigment]. The goal of this investigation was to measure the action spectra and absolute sensitivities of the UV-cone- and M-cone-driven b-wave responses of C57BL/6 mice. To achieve this goal, we suppressed rod-driven signals with steady or flashed backgrounds and obtained intensity-response relations for cone-driven b-waves elicited by narrowband flashes between 340 and 600 nm. The derived cone action spectra can be described as retinal1 pigments with peaks at 355 and 508 nm. The UV peak had an absolute sensitivity of approximately 8 nV/(photon microm2) at the cornea, approximately fourfold higher than the M peak. In an attempt to isolate UV-cone-driven responses, it was discovered that an orange conditioning flash (lambda > 530 nm) completely suppressed ERG signals driven by both M pigment- and UV pigment-containing cones. Analysis showed that the orange flash could not have produced a detectable response in the UV-cone pathway were their no linkage between M pigment- and UV pigment-generated signals. Because cones containing predominantly the UV and M pigments have been shown to be located largely in separate parts of the mouse retina (), the most probable linkage is coexpression of M pigment in cones primarily expressing UV pigment. New histological evidence supports this interpretation (). Our data are consistent with an upper bound of approximately 3% coexpression of M pigment in the cones that express mostly the UV pigment.     

Localized and transient elevations of intracellular Ca2+ induce the dedifferentiation of axonal segments into growth cones

The formation of a growth cone at the tip of a severed axon is a key step in its successful regeneration. This process involves major structural and functional alterations in the formerly differentiated axonal segment. Here we examined the hypothesis that the large, localized, and transient elevation in the free intracellular calcium concentration ([Ca2+]i) that follows axotomy provides a signal sufficient to trigger the dedifferentiation of the axonal segment into a growth cone. Ratiometric fluorescence microscopy and electron microscopy were used to study the relations among spatiotemporal changes in [Ca2+]i, growth cone formation, and ultrastructural alterations in axotomized and intact Aplysia californica neurons in culture. We report that, in neurons primed to grow, a growth cone forms within 10 min of axotomy near the tip of the transected axon. The nascent growth cone extends initially from a region in which peak intracellular Ca2+ concentrations of 300-500 microM are recorded after axotomy. Similar [Ca2+]i transients, produced in intact axons by focal applications of ionomycin, induce the formation of ectopic growth cones and subsequent neuritogenesis. Electron microscopy analysis reveals that the ultrastructural alterations associated with axotomy and ionomycin-induced growth cone formation are practically identical. In both cases, growth cones extend from regions in which sharp transitions are observed between axoplasm with major ultrastructural alterations and axoplasm in which the ultrastructure is unaltered. These findings suggest that transient elevations of [Ca2+]i to 300-500 microM, such as those caused by mechanical injury, may be sufficient to induce the transformation of differentiated axonal segments into growth cones.     

Fabrication and gain performance of Er3+/Yb3+-codoped tellurite glass fiber

Er3+/Yb3+-codoped TeO2-ZnO-BaO-La2O3 tellurite glass fiber was fabricated by rotation and rod-in-tube technologies. The ther-mal stability and optical refractive index of the core and cladding glasses were determined by DTA and optical coupler, respectively. The av-erage background loss of tellurite glass fiber was 1.8 dB/m at 1310 nm. Optical microscopy and field emission scanning electron microscope (FESEM) were used to study structural characteristics of preforms and optical fibers. The main loss of tellurite glass fiber could be attributed to scatter centre due to core-cladding interface defects. The amplifier performance of tellurite glass fiber was investigated by pumping with 980 nm laser diode (LD). The gain coefficient and maximum signal gain were 0.21 dB/mW and 10 dB, respectively, for a pumping power of 120 mW. Gains exceeding 5 dB were obtained over 30 um bandwidth from 1535 to 1565 nm. The minimum noise figure was 4.8 dB at 1557 um.     

The trkA receptor mediates growth cone turning toward a localized source of nerve growth factor

We have developed an in vitro system for studying the interaction of chick dorsal root ganglion neuronal growth cones with a localized source of nerve growth factor (NGF) covalently conjugated to polystyrene beads. Growth cones rapidly turned and migrated under NGF-coated beads in a process that involved the initial formation of persistent contact with a bead, followed by directed flow of cytoplasm toward the point of contact. A role for the local activation of the high-affinity NGF receptor trkA was suggested by a strong inhibition of the turning response by (1) the addition of an antibody against the extracellular portion of trkA, (2) the elevation of the background concentration of NGF to saturate trkA, or (3) the presence of a concentration of the drug K252a that inhibits trkA activation. NGF binding to the pan-neurotrophin receptor p75 is also involved but is not required for turning. These data show a new role for both the trkA and the p75 receptors: the mediation of local events in the guidance of nerve growth cones.     

Inter-individual differences in binaural detection of low-frequency or high-frequency tonal signals masked by narrow-band or broadband noise

Detection thresholds for either 500-Hz tones or 4-kHz tones were measured for a group of 19 listeners utilizing the interaural configurations NoSo and NoS pi. Both broadband (100-8500 Hz) noises and narrow-band (50-Hz-wide) noises served as maskers. In addition, direct measures of the listeners' sensitivities to changes in interaural temporal differences (ITDs) and interaural intensitive differences (IIDs) were measured using 400-Hz-wide noises centered at 500 Hz or 4 kHz. A rather large range of inter-individual differences in threshold was observed for 4-kHz tonal signals masked by narrow-band noise in the NoS pi configuration. This result is consistent with several sets of data from our previous experiments conducted over more than a decade. A broad range of thresholds was also obtained for 500-Hz tonal signals masked by narrow-band noise in the NoS pi configuration. This outcome, coupled with the fact that the use of a broadband masker did not yield a large distribution of thresholds for the detection of a 500-Hz tone masked by a broad band of noise, suggests that it is the use of a narrow-band masker, per se, that results in a large range of thresholds. Statistical analyses revealed that thresholds in the NoS pi detection tasks were not highly correlated with thresholds measured in the ITD- and the IID-discrimination tasks. Nevertheless, the five listeners who were the most sensitive in the narrow-band NoS pi detection and the five listeners who were the least sensitive in the narrow-band NoS pi detection tasks were those who were the most and least sensitive, respectively, to changes in ITDs and to changes in IIDs.     

Fabrication and gain performance of Er^3＋/Yb^3＋-codoped tellurite glass fiber

Er^3＋/Yb^3＋-codoped TeO2-ZnO-BaO-La2O3 tellurite glass fiber was fabricated by rotation and rod-in-tube technologies. The thermal stability and optical refractive index of the core and cladding glasses were determined by DTA and optical coupler, respectively. The average background loss of tellurite glass fiber was 1.8 dB/m at 1310 nm. Optical microscopy and field emission scanning electron microscope （FESEM） were used to study structural characteristics of preforms and optical fibers. The main loss of tellurite glass fiber could be attributed to scatter centre due to core-cladding interface defects. The amplifier performance of tellurite glass fiber was investigated by pumping with 980 nm laser diode （LD）. The gain coefficient and maximum signal gain were 0.21 dB/mW and 10 dB, respectively, for a pumping power of 120 mW. Gains exceeding 5 dB were obtained over 30 nm bandwidth from 1535 to 1565 nm. The minimum noise figure was 4.8 dB at 1557 nm.     

Self-thermostatting organically coated steel cladding using thermochromic materials

Abstract

This paper explores the effect of colour and gloss on the solar/thermal gain achieved by organically coated steels (OCSs) under external and artificial exposure conditions. External and artificial exposure tests have shown that the colour of an organic coating has a dramatic effect on the thermal gain. Otherwise identical black and white panel assemblies have been found to experience average thermal gains of 16 K and 1·6 K, respectively, over a typical UK daylight exposure. The coating gloss also affects the solar gain but to a much less significant level, with the thermal gain for standard panel colours changing by only 2·5 K when gloss levels are altered between 80 and 10%. Thus, the colour of the organic coating was the most important factor controlling thermal gain. To control solar gain, novel panel assemblies have been prepared in which thermochromic inks with two temperature dependent colours have been incorporated with an OCS topcoat. These have been compared with traditional OCS products, with similar colour and gloss to the two extremes of colour of the novel material. It has been found that as the temperature of the test panels rises and the colour of the organic coating is converted to its lighter shade, the thermal gain of the panel assemblies is lowered and thus the panels have a self-thermostatting capability.